[[software:linux]]
Trace: • video_encoding • ssh • linux

General Linux

strip-roulette-russe-650-finalenglish.jpg

Questions answered

How to emulate mouse on USB?

How to create a virtual/simulated USB Mouse using Raspberry Pi reads that Raspberry Pi can act as USB OTG.

Additionally:

How to uninstall program which was installed using make install?

Use checkinstall.

How to fix cron syslog entry Authentication service cannot retrieve authentication info

In cron log the entry appears:
CRON: Authentication service cannot retrieve authentication info

Run pwck command, as your /etc/passwd is not in sync with /etc/shadow.

How to capture kernel panic log?

The easiest way is to use netconsole kernel module as log transmitter and rsyslog as log receiver on some remote system (e.g. booted as life image). Check Setup netconsole to capture kernel panic logs. Step-by-step instruction:
  • Create

    /etc/modprobe.d/netconsole.conf

    # Enable remote kernel logging.
# netconsole=<LOCAL_PORT>@<SENDER_IP_ADDRESS>/[SENDER_INTERFACE],<REMOTE_PORT>@<RECEIVER_IP_ADDRESS>/[MAC_ADDRESS]
options netconsole netconsole=6666@192.168.5.1/br0,514@192.168.5.100/

    Note that MAC address is optional, however trailing slash is obligatory.

  • Do modprobe netconsole – it should result the following in dmesg: 
    netpoll: netconsole: local port 6666
netpoll: netconsole: local IPv4 address 192.168.5.1
netpoll: netconsole: interface 'br0'
netpoll: netconsole: remote port 514
netpoll: netconsole: remote IPv4 address 192.168.5.100
netpoll: netconsole: remote ethernet address ff:ff:ff:ff:ff:ff
console [netcon0] enabled
netconsole: network logging started

    If module fails with the message netpoll: (null): eth1 doesn't support polling, aborting then remove the conflicting interface from the bridge.

  • After that on remote PC (192.168.5.100) run nc -lu 514 | tee -a dmesg.log to capture kernel messages.

See also:

How to capture core dumps?

Install systemd-coredump (which installs /etc/sysctl.d/60-coredump.conf that does the magic) and modify /etc/systemd/coredump.conf.

This post also suggests to modify /etc/security/limits.conf and add 

* hard core unlimited

to it.

See also:

How to format dmesg timestamps?

The time given in dmesg is in seconds since kernel startup, so the time from /proc/uptime needs to be added: 
dmesg | perl -w -Mstrict -MPOSIX -e 'my $uptime = $1 if `cat /proc/uptime` =~ /^(\d+)\./;
foreach my $line (<>) {
    printf($line =~ /^\[\s*(\d+)\.\d+\](.+)/
        ? "[" . strftime("%F %T", localtime(time() - $uptime + $1)) . "]$2\n"
        : $line
    );
}'

Or simply use dmesg -T.

See Convert dmesg timestamp to custom date format and How to convert 'dmesg' time format to 'real' time format.

How to view boot log of the previous system run?

Boot logs are not dumped to /var/log/boot in systemd-based distributive, as they are managed by journalctl. However the last one does not flush logs into persistent location. In order to force that, set Storage=persistent in /etc/systemd/journald.conf and run systemctl restart systemd-journald. After that you will be able to see logs for boots in the past (performed after the option was applied): 
# journalctl --list-boots
# journalctl -b1 -o short-precise

How to list all failed systemd units?

systemctl list-units –failed

To further see the last log messages of failed unit:

systemctl -l status some-failed.service

It can happen that the service that causes the ordering cycle is disabled (kicked-off) to break the cycle. To investigate such service:
# systemd-analyze verify default.target

should not display something like that: 

Found ordering cycle on systemd-tmpfiles-setup.service/start
Found dependency on local-fs.target/start
Found dependency on problematic.service/start
Found dependency on sysinit.target/start
Job systemd-tmpfiles-setup.service/start deleted to break ordering cycle starting with sysinit.target/start
# systemctl show -p Requires,Wants,Requisite,BindsTo,PartOf,Before,After problematic-service.target
# systemd-analyze dot problematic-service.target other.target | dot -Tsvg > cycle.svg

MySQL does not stop under systemd

Follow advice give in here. After upgrading MySQL to v5.7, the problem should go away.

How to set up a runlevel in Debian?

Alternatives:
  • Works for all environments: edit /etc/default/grub and add 3 to the end of kernel line: GRUB_CMDLINE_LINUX_DEFAULT="quiet 3". Refresh grub (run update-grub).
  • For SysV init edit /etc/inittab and set value 3 to 2nd column of the line i.e. id:3:initdefault:
  • For systemd-driven environment run cd /etc/systemd/system && ln -sf /lib/systemd/system/multi-user.target default.target

How to program what power button does?

ACPI functions have been taken over by systemd. Edit /etc/systemd/logind.conf and set e.g. 
[Login]
HandleLidSwitch=ignore
HandleLidSwitchDocked=ignore

to ignore closing the notebook lid or 

[Login]
HandlePowerKey=ignore

to ignore power button press and then run service systemd-logind restart.

See also:

Outdated

How to save battery power on Laptop?

From Как продлить время работы ноутбука с Ubuntu:

What is ASPM?

From What does “r8169: can't disable ASPM; OS doesn't have ASPM control” really mean?: 
# fwts aspm; cat report.log

Test 1 of 2: PCIe ASPM ACPI test.
SKIPPED: Test 1, No valid FACP information present: cannot test ASPM.

Test 2 of 2: PCIe ASPM registers test.
WARNING: Test 2, RP 0000h:00h:1Ch.00h L0s not enabled.
WARNING: Test 2, Device 0000h:01h:00h.00h L0s not enabled.

ADVICE: The ASPM L0s low power Link state is optimized for short entry and exit
latencies, while providing substantial power savings. Disabling L0s of a PCIe
device may increase power consumption, and will impact the battery life of a
mobile system.

PASSED: Test 2, PCIe ASPM setting matched was matched.
WARNING: Test 2, RP 0000h:00h:1Ch.03h L0s not enabled.
WARNING: Test 2, Device 0000h:03h:00h.00h L0s not enabled.

ADVICE: The ASPM L0s low power Link state is optimized for short entry and exit
latencies, while providing substantial power savings. Disabling L0s of a PCIe
device may increase power consumption, and will impact the battery life of a
mobile system.

PASSED: Test 2, PCIe ASPM setting matched was matched.

See also:

How to list all libraries loaded by a process?

pldd <pid> or pmap 6297 | grep .so | cut -c24- | sort -u

Where is X11 session autostart?

  • When starting VNC server then ~/.vnc/xstartup otherwise ~/.xsessionrc (~/.Xtigervnc-session for TigerVNC), see Xsession and Autostarting.
  • Xfce session is stored in session cache in ./.cache/sessions/xfce4-session-* and managed from Settings → Session and Startup → Session tab.

Where is desktop autostart?

Check .config/autostart or .kde/Autostart directory.

How to send POST HTTP request using cURL?

From What is the cURL command-line syntax to do a POST request:

curl -X POST --header "Content-Type:text/xml" -d @filename.xml http://example.com/path/to/resource

Another example with:

  • -s to disable progress indicator
  • -v to print headers (is better than -D -)
  • –raw to see original (not decoded) message, e.g. when the message is chunked
  • –negotiate -u : to enable SPNEGO authentication

curl -s -v --raw --negotiate -u : -X POST --header 'Content-Type: application/json' --header 'Accept: application/json' -d '{ "field": 1 }' 'http://server.org/path'

How to force diff to ignore different newline presentation (CR/LF)?

As to Prevent diff from checking for newline at end of file and How do I get patch to ignore carriage returns there is no straightforward solution to the problem: if one needs to ignore only newlines, the files should be first pre-processed. But more general solution would be to use --ignore-all-space option:

diff --ignore-all-space file1 file2

How to remove BOM from the text file?

Use dos2unix.

''cut -c'' (''--characters'') does not work with UTF-8 

$ echo 'αβγ' | cut -c 3-4
β

Use solutions which are based on

Console

How to disable printing of kernel messages to console?

dmesg -n 1 or (for recent versions) dmesg -D

How allocate tty1 to display syslog output?

  • Run systemctl stop getty@tty1.service then systemctl disable getty@tty1.service
  • Uncomment/add the following to /etc/systemd/journald.conf
ForwardToConsole=yes
TTYPath=/dev/tty1
MaxLevelConsole=info

Didn't work:

Change ACTIVE_CONSOLE=“dev/tty[2-4]” in /etc/default/console-setup and run dpkg-reconfigure console-setup, see:

How to disable cleaning of first console after boot?

From Disable Clearing of Boot Messages:

In /etc/inittab add the --noclear option for the configuration line (starts with c1) of first virtual console: 

c1:2345:respawn:/sbin/agetty --noclear -8 38400 tty1 linux

For systemd check Stop Clearing My God Damned Console: 

# mkdir /etc/systemd/system/getty@.service.d
# cat > /etc/systemd/system/getty@.service.d/noclear.conf <<'EOF'
[Service]
TTYVTDisallocate=no
EOF
# systemctl daemon-reload

How to enable monitor standby in console?

setterm –blank 2

How to monitor the progress of byte-stream copy?

  • dd if=/dev/urandom | pv | dd of=/dev/null
  • Rub dd in one console and in another run kill -USR1 $(pgrep ^dd)

Alternative is progress – Linux tool to show progress for cp, mv, dd, … which monitors open filedesciptors in /proc to display the progress.

How to control coloring of ls output?

From ls colors and dircolors: modify color settings globaly:

export LS_COLORS='no=00:fi=00:di=05;33:ln=01;36:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:r=40;31;01:ex=01;32.tar

How to recover occasionally deleted tmux pipe / session?

According to the tmux mapage:

If the socket is accidentally removed, the SIGUSR1 signal may be sent to the tmux server process to recreate it.

So sending the signal and attaching works: 

$ killall -s SIGUSR1 tmux
$ tmux attach

How to fix the problem with missing locale?

The following is reported to console: 
perl: warning: Please check that your locale settings:
        LANGUAGE = "en_US:en",
        LC_ALL = (unset),
        LC_MESSAGES = "en_US.UTF-8",
        LANG = "en_US.UTF-8"
    are supported and installed on your system.

  • Check that /etc/default/locale has a correct locale setting. If not, run update-locale LANGUAGE=en_US.UTF-8 to update it.
  • Check that desired locale en_US.UTF-8 is present in /etc/locale.gen (grep en_US.UTF-8 /etc/locale.gen). If not, run locale-gen en_US en_US.UTF-8 && dpkg-reconfigure locales to generate it.

Security

Strange log message from pam_ldap

I have configured pam_ldap module correctly, but still this lines in log file
sshd[29284]: pam_ldap: error trying to bind as user "cn=jack,cn=users,dn=domain" (Invalid credentials)

Dummy, but authentication does not work correctly until libnss-ldap is installed and configured correctly.

How to implement LDAP-based authentication?

For example, I want to check the supplied user's password and that the user belongs to some particular LDAP group.

Implementation of LDAP service usage

This is currently implemented only in Apache mod_authnz_ldap module. You need to enable Require valid-user and Require ldap-group. After reading the following documentation on search filtering (String Representation of Search Filters, LDAP: Matching Rule Identifier, LDAP Attribute Syntax Definitions, LDAP Search Filters1), Правила соответствия) and trying to find the extended matching rule (like this2), I came to the conclusion that this search cannot be done via one filter. During the first search the module should learn the dn of a user by it's uid or email, and then use the located dn to search in a specific group. To make things more simple I suggest to define dummy object classes to define a list of authorized services and use this object class in a filter. Examples:

LDAP schema (/etc/ldap/schema/centurion.schema)

objectclass ( 1.3.6.1.4.1.1000.0 NAME 'commonAccount' SUP top ABSTRACT
    DESC 'General account account'
    MUST ( uid $ userPassword ) )

objectClass ( 1.3.6.1.4.1.1000.1 NAME 'apacheAccount' SUP commonAccount AUXILIARY
    DESC 'Apache htpasswd account' )

objectClass ( 1.3.6.1.4.1.1000.2 NAME 'dokuwikiAccount' SUP commonAccount AUXILIARY
    DESC 'Dokuwiki account' )

objectClass ( 1.3.6.1.4.1.1000.3 NAME 'mailAccount' SUP commonAccount AUXILIARY
    DESC 'Cyrus/Postfix account' )

objectClass ( 1.3.6.1.4.1.1000.4 NAME 'proftpdAccout' SUP commonAccount AUXILIARY
    DESC 'ProFTPd account' )

Apache mod_authnz_ldap (/etc/apache2/sites-enabled/001-default-ssl)

<IfModule mod_authn_alias.c>
    <AuthnProviderAlias ldap ldap-auth-provider>
        AuthLDAPURL "ldap://localhost:389/cn=persons,cn=centurion?uid?one?(objectClass=apacheAccount)"
    </AuthnProviderAlias>
</IfModule>
<VirtualHost _default_:443>
    Alias /dav/ /var/lib/dav/
    <Location /dav>
        DAV on
 
        AuthType Basic
        AuthName "DAV Storage"
 
        AuthBasicProvider ldap-auth-provider
 
        Options Indexes
 
        <LimitExcept GET HEAD OPTIONS>
            Require valid-user
        </LimitExcept>
    </Location>
</VirtualHost>

dokuwiki auth_ldap (conf/dokuwiki.php)

$conf['useacl']      = 1;
$conf['autopasswd']  = 0;
$conf['authtype']    = 'chained';
$conf['auth']['chained']['authtypes'] = 'plain,ldap';
$conf['auth']['ldap']['server']       = 'ldap://localhost:389';
$conf['auth']['ldap']['usertree']     = 'cn=persons,cn=centurion';
$conf['auth']['ldap']['userfilter']   = '(&(objectClass=dokuwikiAccount)(uid=%{user}))';
$conf['auth']['ldap']['grouptree']    = 'cn=groups,cn=centurion';
$conf['auth']['ldap']['groupfilter']  = '(member=%{dn})';
$conf['auth']['ldap']['version']      = 3;
$conf['passcrypt']   = 'ssha';
$conf['defaultgroup']= 'dokuwiki';

Similar ProFTPd topics: 1, 2, 3. Also take in mind this bug, which effectively breaks the authentication via LDAP, and which was solved in proftpd-basic_1.3.2-1.

ProFTPd mod_ldap (/etc/proftpd/ldap.conf)

<IfModule mod_ldap.c>
LDAPServer ldap://localhost
LDAPSearchScope onelevel
LDAPDoAuth on "cn=persons,cn=centurion" "(&(objectclass=proftpdAccount)(uid=%v))"
LDAPAuthBinds on
</IfModule>

Samba server can be switched to using LDAP the following way3):

Samba configuration (/etc/samba/smb.conf)

passdb backend = ldapsam:ldap://localhost
ldap suffix = cn=centurion
ldap user suffix = cn=persons,cn=centurion
ldap group suffix = cn=groups,cn=centurion
# The password for this user is stored in secrets.tdb. It is set by running 'smbpasswd -w passwd':
ldap admin dn = cn=ldapadmin,cn=centurion

Samba should have permissions to add sambaSamAccount object class to existing person and initialize needed attributes. Cyrus IMAP sevice authenticates itself via saslauthd:

saslauthd /etc/saslauthd.conf

ldap_servers: ldap://localhost
ldap_search_base: cn=persons,cn=centurion
ldap_filter: (&(objectClass=mailAccount)(uid=%u))
ldap_scope: one

pam_ldap (/etc/pam_ldap.conf)

base             cn=centurion
uri              ldap://127.0.0.1/
ldap_version     3
rootbinddn       cn=ldapadmin,cn=centurion
scope            sub
pam_filter       objectClass=shadowAccount
pam_password     exop
nss_base_passwd  cn=persons,cn=centurion?one
nss_base_shadow  cn=persons,cn=centurion?one
nss_base_group   cn=groups,cn=centurion?one

PAM is configurable via pam-auth-update. Generally you have to add pam_ldap.so to your PAM configuration (see /usr/share/doc/libpam-ldap/examples/pam.conf).

Also you should take in mind, that if some services need the availability of user ID at startup, they need to start after LDAP server. For example, for cron one should add the following lines to init.d script:

Cron (/etc/init.d/cron)

...
### BEGIN INIT INFO
# Provides:          cron
...
# Should-Start:      slapd
# Should-Stop:       slapd
...

How to add schemas to OpenLDAP?

From How to add a new schema to openldap 2.4.11 and from 6.1.1.4.2 Add/Delete Schemas using OLC → slaptest Conversion
  1. Stop OpenLDAP server:
    /etc/inid.d/slapd stop
  2. Create file schema_import.conf like this:

    schema_import.conf

    include /etc/ldap/schema/core.schema
include /etc/ldap/schema/cosine.schema
include /etc/ldap/schema/nis.schema
include /etc/ldap/schema/inetorgperson.schema
include /etc/ldap/schema/mozilla.schema
include /etc/ldap/schema/samba.schema
  3. Run slaptest to convert *.schema to *.ldif:
    mkdir /tmp/ldap_import; slaptest -f schema_import.conf -F /tmp/ldap_import
  4. Copy necessary files to /etc/ldap/slapd.d/cn=config/cn=schema giving them correct numbering:
    mv /tmp/ldap_import/cn={4}mozilla.ldif /etc/ldap/slapd.d/cn\=config/cn\=schema\cn\={5}mozilla.ldif
    mv /tmp/ldap_import/cn={5}samba.ldif /etc/ldap/slapd.d/cn\=config/cn\=schema\cn\={6}samba.ldif
  5. Start OpenLDAP server:
    /etc/inid.d/slapd start

How to add index to the database in OpenLDAP?

The following will create index on memberUid for the database {1}mdb: 
# ldapmodify -H ldapi:// -Y EXTERNAL <<'EOF'
dn: olcDatabase={1}mdb,cn=config
add: olcDbIndex
olcDbIndex: memberUid eq
EOF
SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
modifying entry "olcDatabase={1}mdb,cn=config"

To verify check slapcat -s olcDatabase={1}mdb,cn=config output.

How to fix the error "ldif_read_file: checksum error" in OpenLDAP?

  • Copy the given .ldif file and remove the header lines (auto-generated comments): 
    # AUTO-GENERATED FILE - DO NOT EDIT!! Use ldapmodify.
# CRC32 61e6182a
  • Calculate CRC32 using crc32 utility from libarchive-zip-perl package (see How to check crc of a file?).
  • Put the resulting value into the header of original .ldif file.

Note that from v2.4.23-3 the configuration of OpenLDAP has been changed to LDIFF in /etc/ldap/slapd.d, see OpenLDAP Setup.

passwd command fails

passwd command fails with the following message: 
# passwd someuser
passwd: Authentication information cannot be recovered
passwd: password unchanged

Remove use_authtok from pam_ldap.so configuration in /etc/pam.d/common-password4)

ldapsearch -x -ZZ fails with a following error: ldap_start_tls: Connect error (-11)

Self-signed certificate results: 
ldap_sasl_bind(SIMPLE): Can’t contact LDAP server (-1)

Unknown certificate results: 

ldap_start_tls: Connect error (-11)

Try to run ldapsearch -h your.server.fqdn -x -d 127 -LLL -ZZ. If it says TLS: peer cert untrusted or revoked then it means the server returns the certificate, which cannot be verified by the client. To fix do the following:
  • Add TLS_CACERT /etc/ssl/certs/ca-certificates.crt to your /etc/ldap/ldap.conf5).
  • Appended necessary certificate to that file (cat my.crt >> /etc/ssl/certs/ca-certificates.crt)6)

Alternatively one can add TLS_REQCERT never to his ~/.ldaprc.

See also Cannot connect to LDAP server via ldaps protocol.

slapd daemon fails to start with message main: TLS init def ctx failed: -1

Make sure that configuration options olcTLSCertificateFile and olcTLSCertificateKeyFile point to readable by OpenLDAP user file (e.g. readable by group openldap).

Network and wireless

For mail-related questions see Postfix and Cyrus.

How to rename network interfaces?

Choose one of the methods:

:INFO: To reload udev rules run udevadm control --reload-rules && udevadm trigger

:INFO: To monitor events, use udevadm monitor -e

:INFO: To rename interface use ip link set wlp1s0 name wlan0

References:

See man socat.

What does RUNNING in ifconfig output mean?

It means there is a network link to a remote device, i.e. the cable is plugged in.

How to implement source-based routing?

Suppose one wants to use different default route (192.168.1.200) for packets that originate from IP address 192.168.1.10. In below example this is the IP address of eth1 however interface could have other IP address. From command line this is done like this:
# echo -e "1\teth1.route" >> /etc/iproute2/rt_tables
# ip rule add from 192.168.1.10 table eth1.route
# ip route add default via 192.168.1.200 dev eth1 table eth1.route

and corresponding Debian setting is:

/etc/network/interfaces

iface eth1 inet static
    address 192.168.1.10
    up ip rule add from 192.168.1.10 table eth1.route
    up ip route add default via 192.168.1.200 dev eth1 table eth1.route

What is the flow of the packets in iptables?

See iptables packet flow.

How to offer a proxy server via DHCP?

From How to configure auto proxy via DHCP? and Deploying Proxy Settings Through DHCP:

/etc/dhcp/dhcpd.conf

option wpad-config code 252 = text;
...
subnet 192.168.0.0 netmask 255.255.0.0 {
    ...
    option wpad-config "http://your.web.server/wpad";
}

wpad

function FindProxyForURL(url, host) {
    if (shExpMatch(host, "192.168.*")
        || shExpMatch(host, "127.*")
        || shExpMatch(host, "localhost")
        || shExpMatch(host, "*.domain.local")
        || shExpMatch(host, "*.home")
        || isPlainHostName(host)
        || dnsDomainIs(host, ".domain.local")) {
        return "DIRECT";
    }
    if (isInNet(host, "192.168.0.0", "255.255.0.0")) {
        return "DIRECT";
    }
    return "PROXY your.proxy.server:3128; DIRECT";
}

How to generate QR code for WiFi network connection?

qrencode -l M -m 0 -o wifi.png "WIFI:S:<SSID>;T:<WEP|WPA>;P:<password>;;"

How to improve WiFi performance?

  • Use the channel the interferes less with neighbouring AP:
    iwconfig wlan0 channel 11
  • Split packets into smaller sizes:
    iwconfig wlan0 frag 256
  • Switch off rts handshaking:
    iwconfig wlan0 rts 1
  • Increase the number of retries:
    iwconfig wlan0 retry 30
  • Don't request or claim the address by ARP:
    dhdpcd -A wlan0

References:

What are the WiFi USB dongles that support master mode?

Does Realtek RTL8187 support master mode?

rtl8187 driver page and another rtl8187 page state that AP/Master mode is not working. This is true for Linux driver in mainline.

When trying to set the card to AP mode the following error is returned: 

# iwconfig wlan0 mode master
Error for wireless request "Set Mode" (8B06) :
    SET failed on device ra0 ; Invalid argument.

meaning that the card doesn't support master mode. However Aircrack Realtek RTL8187L ieee80211-based driver (but README.FIRST in r8187b-2.6.25-hirte.tar.bz2 reads that driver is for RTL8187B) claims that it supports AP. There are same rtl8187 driver sources which are adapted for Linux 3.8.

Other notes from maillists below:

  • RTL8187L chip only has a single hardware transmit queue and the work of getting the high-priority traffic, such as beacons, transmitted at the correct time would be much more than it would be worth. Will the device be able to transmit beacons with an appropriate timing accuracy?
  • The module in kernel is using mac80211 wireless stack while the module from Realtek website does not use it.
  • To modify the driver, you will need to study some other driver that does work in master mode.
  • There were some discussion a while back that some generic master mode support for all mac80211-based drivers might eventually happen.

References:

Error when trying to switch Atheros card to master mode

When trying to switch Atheros card to master mode to setup WiFi Access Point, the following error occurs:
# iwconfig wlan0 mode master
Error for wireless request "Set Mode" (8B06) :
    SET failed on device wlan0 ; Invalid argument.

In general Atheros-based cards seems to be the best choice for master mode / access point solution, check ath9k supported devices (more) and ath10k supported devices (more) for example, AR5B22/AR9462-based cards on eBay.

:WARN: Information below is outdated as ath5k module supports master mode (AP).

ath5k module info

athk WiFi AP mode problem: After joining two interface into a bridge, DHCP packets do not go from wlan0 to eth1 interface, so the WiFi client cannot join the network.

See answers here and here

What is “wmaster0”?

See answers here and here

How to install Windows driver into Linux using NDISwrapper?

For example let's install NDIS driver for USB RTL8187 Wifi dongle. When you plug it in, you see in dmesg: 
usb 1-1: new high-speed USB device number 2 using ehci_hcd
usb 1-1: New USB device found, idVendor=0df6, idProduct=000d
usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-1: Product: RTL8187_Wireless_LAN_Adapter
usb 1-1: Manufacturer: Manufacturer_Realtek_RTL8187_
usb 1-1: SerialNumber: 000CF63A630A

When you do this, you see in dmesg the following: 

ndiswrapper version 1.57 loaded (smp=no, preempt=no)
ndiswrapper: driver rtl8187a (Realtek Semiconductor Corp.,06/13/2008,5.1313.0613.2008) loaded
wlan0: ethernet device 00:0c:f6:3a:63:0a using NDIS driver: rtl8187a, version: 0x1, NDIS version: 0x500, vendor: 'Realtek RTL8187 Wireless LAN USB NIC', 0DF6:000D.F.conf
wlan0: encryption modes supported: WEP; TKIP with WPA, WPA2, WPA2-PSK; AES/CCMP with WPA, WPA2, WPA2-PSK
usbcore: registered new interface driver ndiswrapper

and your wlan0 interface is ready to be configured in normal way.

ndiswrapper does not support master mode.

How to list all SSL ciphers?

To list all ciphers that locally installed OpenSSL supports use:

openssl ciphers -v

or the same, but with filtering:

openssl ciphers -v 'HIGH:!SSLv2:!SSLv3:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!PSK:!MD5:@STRENGTH'

To list all ciphers that the service supports, use nmap ssl-enum-ciphers: 

# nmap --script ssl-enum-ciphers -p 443 127.0.0.1
Starting Nmap 6.47 ( http://nmap.org ) at 2014-10-18 19:37 CEST
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00013s latency).
PORT    STATE SERVICE
443/tcp open  https
| ssl-enum-ciphers:
|   SSLv3: No supported ciphers found
|   TLSv1.0:
|     ...
|   TLSv1.1:
|     ...
|   TLSv1.2:
|     ciphers:
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 - strong
|       TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 - strong
|       TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 - strong
|       TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 - strong
|       TLS_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_RSA_WITH_AES_128_CBC_SHA256 - strong
|       TLS_RSA_WITH_AES_128_GCM_SHA256 - strong
|       TLS_RSA_WITH_AES_256_CBC_SHA - strong
|       TLS_RSA_WITH_AES_256_CBC_SHA256 - strong
|       TLS_RSA_WITH_AES_256_GCM_SHA384 - strong
|     compressors:
|       NULL
|_  least strength: strong

To test if service supports given cipher, use:

openssl s_client -host localhost -port 993 -cipher 3DES

See also:

How to verify the fingerprint of the site?

On the server side one needs an access to certificate file: 
# openssl x509 -in server.pem -fingerprint -noout [-sha256]
SHA1 Fingerprint=30:46:D3:11:DC:8E:66:8B:36:8E:61:DB:DB:65:11:66:D8:6E:50:21

and on the client side it should result the same fingerprint: 

# openssl s_client -connect host:443 | openssl x509 -fingerprint -noout
depth=4 C = US, ST = UT, L = Salt Lake City, O = The USERTRUST Network, OU = http://www.usertrust.com, CN = UTN - DATACorp SGC
verify error:num=19:self signed certificate in certificate chain
verify return:0
SHA1 Fingerprint=30:46:D3:11:DC:8E:66:8B:36:8E:61:DB:DB:65:11:66:D8:6E:50:21

How to connect bluetooth keyboard

  • Install bluez: 
    # apt-get install bluez
  • Make sure that your bluetooth dongle is detected: 
    # dmesg
Bluetooth: Core ver 2.16
Bluetooth: HCI device and connection manager initialized
Bluetooth: HCI socket layer initialized
Bluetooth: L2CAP socket layer initialized
Bluetooth: SCO socket layer initialized
Bluetooth: Generic Bluetooth USB driver ver 0.6
Bluetooth: RFCOMM TTY layer initialized
Bluetooth: RFCOMM socket layer initialized
Bluetooth: RFCOMM ver 1.11
Bluetooth: BNEP (Ethernet Emulation) ver 1.3
Bluetooth: BNEP filters: protocol multicast# hcitool dev
# lsusb
Bus 003 Device 003: ID 0a12:0001 Cambridge Silicon Radio, Ltd Bluetooth Dongle (HCI mode)
# hcitool dev
Devices:
        hci0    00:1A:7D:DA:71:15
  • Put the keyboard in discoverable mode and ensure you can see it 
    # hcitool scan
Scanning ...
        20:12:08:9A:18:20       Bluetooth keyboard for ipad
  • Pair with keyboard (1234 is entered and passed to keyboard where one should type it and press Enter) and connect to it: 
    # bluez-simple-agent hci0 20:12:08:9A:18:20
RequestPinCode (/org/bluez/27229/hci0/dev_20_12_08_9A_18_20)
Enter PIN Code: 1234
Release
New device (/org/bluez/27229/hci0/dev_20_12_08_9A_18_20)
# bluez-test-device trusted 20:12:08:9A:18:20 yes
# bluez-test-input connect 20:12:08:9A:18:20

    In bluez v5.23 and later the same should be performed using bluetoothctl: 

    # bluetoothctl
[bluetooth]# pair 20:12:08:9A:18:20
  • Verify the connection: 
    # hcitool con
Connections:
        < ACL 20:12:08:9A:18:20 handle 71 state 1 lm MASTER AUTH ENCRYPT
# dmesg
Bluetooth: HIDP (Human Interface Emulation) ver 1.2
input: Bluetooth keyboard for ipad as /devices/pci0000:00/0000:00:1d.1/usb3/3-2/3-2:1.0/bluetooth/hci0/hci0:71/input13
generic-bluetooth 0005:05AC:023C.000C: input,hidraw1: BLUETOOTH HID v6.44 Keyboard [Bluetooth keyboard for ipad] on 00:1A:7D:DA:71:15
  • In case the pairing should automatically happen during the boot, add the following:

    /etc/bluetooth/rfcomm.conf

    rfcomm0 {
    bind yes;
    device 20:12:08:9A:18:20;
    comment "Bluetooth keyboard for ipad";
}

    In latest bluez versions the same should be performed using bluetoothctl: 

    # bluetoothctl
[bluetooth]# trust 20:12:08:9A:18:20
  • Remove the pairing: 
    # bluez-simple-agent hci0 20:12:08:9A:18:20 remove

    In latest bluez versions the same should be performed using bluetoothctl: 

    # bluetoothctl
[bluetooth]# remove 20:12:08:9A:18:20

See also:

Video

How to watch DVB-T TV channels?

xine in action xine in action

  • Buy module from DVB-T USB devices list. I have DiBcom STK 7770P that comes with Dune HD. Make sure it is connected to PC: 
    $ lsusb
Bus 001 Device 002: ID 10b8:1e80 DiBcom
  • Install firmware-linux-nonfree. That will place dvb-usb-dib0700-1.20.fw into /lib/firmware. Alternatively you can download it from here.
  • Reboot the system. This is required for firmware agent to load firmware needed by driver to the device.

    dmesg

    usb 1-4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-4: Product: STK7770P_v1-4
usb 1-4: Manufacturer: DiBcom
usb 1-4: SerialNumber: 005
dvb-usb: found a 'DiBcom STK7770P reference design' in cold state, will try to load a firmware
usb 1-4: firmware: agent loaded dvb-usb-dib0700-1.20.fw into memory
dvb-usb: found a 'DiBcom STK7770P reference design' in warm state.
dvb-usb: will pass the complete MPEG2 transport stream to the software demuxer.
dvb-usb: schedule remote query interval to 50 msecs.
dvb-usb: DiBcom STK7770P reference design successfully initialized and connected.
usbcore: registered new interface driver dvb_usb_dib0700
  • Install dvb-apps and perform the channel scanning:
    scan /usr/share/dvb/dvb-t/nl-All > channels.conf
    You will see among other staff something like this: 
    >>> tune to: 722000000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_1_2:FEC_AUTO:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_4:HIERARCHY_NONE
0x0000 0x044d: pmt_pid 0x1b62 Digitenne -- Nederland 1 (running)
0x0000 0x044e: pmt_pid 0x1b6c Digitenne -- Nederland 2 (running)
0x0000 0x044f: pmt_pid 0x1b76 Digitenne -- Nederland 3 (running)
0x0000 0x0450: pmt_pid 0x1b80 Digitenne -- TV West (running)
0x0000 0x0457: pmt_pid 0x1bc6 Digitenne -- Radio West (running)
0x0000 0x0458: pmt_pid 0x1bd0 Digitenne -- Radio 1 (running)
0x0000 0x0459: pmt_pid 0x1bda Digitenne -- Radio 2 (running)
0x0000 0x045a: pmt_pid 0x1be4 Digitenne -- 3FM (running)
0x0000 0x045b: pmt_pid 0x1bee Digitenne -- Radio 4 (running)
0x0000 0x045c: pmt_pid 0x1bf8 Digitenne -- Radio 5 (running)
0x0000 0x045d: pmt_pid 0x1c02 Digitenne -- Radio 6 (running)
0x0000 0x045f: pmt_pid 0x1c16 Digitenne -- FunX (running)
Network Name 'Digitenne'
  • Install any player that supports DVB on your wish (Xine, mplayer, Xawtv (v4.x), Me TV7) ).
  • For e.g. xine and mplayer copy the scanned channels information to ~/.xine/channels.conf and ~/.mplayer/channels.conf correspondingly. Launch the player:
    xine "dvb://Nederland 1"

Other links on the topic:

How to setup DLNA server?

See:

How to setup OPDS server?

Checkout:

How to setup framebuffer?

In Intel-based chipsets create
# echo "options i915 modeset=1" > /etc/modprobe.d/framebuffer.conf

and then reboot (most of modules are compiled to kernel). Kernel messages: 

# dmesg | egrep -i '(fb0|vesafb|inteldrmfb|i915|video|console)'
Console: colour dummy device 80x25
pci 0000:00:02.0: Video device with shadowed ROM at [mem 0x000c0000-0x000dffff]
vesafb: mode is 640x480x32, linelength=2560, pages=0
vesafb: scrolling: redraw
vesafb: Truecolor: size=8:8:8:8, shift=24:16:8:0
vesafb: framebuffer at 0xe0000000, mapped to 0x00000000e4f3f729, using 1216k, total 1216k
Console: switching to colour frame buffer device 80x30
fb0: VESA VGA frame buffer device
i915 0000:00:02.0: [drm] PipeC fused off
i915 0000:00:02.0: [drm] VT-d active for gfx access
fb0: switching to inteldrmfb from VESA VGA
Console: switching to colour dummy device 80x25
i915 0000:00:02.0: vgaarb: deactivate vga console
i915 0000:00:02.0: [drm] DMAR active, disabling use of stolen memory
i915 0000:00:02.0: vgaarb: changed VGA decodes: olddecodes=io+mem,decodes=io+mem:owns=io+mem
[drm] Initialized i915 1.6.0 20200917 for 0000:00:02.0 on minor 0
ACPI: Video Device [GFX0] (multi-head: yes  rom: no  post: no)
input: Video Bus as /devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/LNXVIDEO:00/input/input6
snd_hda_intel 0000:00:03.0: bound 0000:00:02.0 (ops i915_audio_component_bind_ops [i915])
i915 0000:00:02.0: [drm] Cannot find any crtc or sizes
fbcon: i915drmfb (fb0) is primary device
Console: switching to colour frame buffer device 240x67
i915 0000:00:02.0: [drm] fb0: i915drmfb frame buffer device

# fbset
mode "1920x1080"
    geometry 1920 1080 1920 1080 32
    timings 0 0 0 0 0 0 0
    accel true
    rgba 8/16,8/8,8/0,0/0
endmode

See also:

X Window Server headless configuration: it is not possible to start X Server without any monitor physically attached to the PC?

The solution is described here:

/etc/X11/xorg.conf

Section "Device"
    Option "NoDDC" true
    Option "NoEDID" "1"
    Option "IgnoreEDID" true
    Driver "i810"
EndSection

Interesting fonts on Debian

Xfce window manager crashes with segfault in libdbus-glib.so 

$ xfce4-session
Bus error

$ xfce4-session
Segmentation fault

$ dmesg | grep xfce4
[Fri Dec  8 20:20:44 2017] xfce4-session[26591]: segfault at 0 ip b6b14900 sp bfbe6bdc error 6 in libdbus-glib-1.so.2.3.3[b6b07000+2a000]

Try to reinstall the packages: 
apt-get install --reinstall xfce4-session libdbus-1-3 libdbus-glib-1-2 libglib2.0-0 libxfce4ui-1-0 libxfce4util7 libxfconf-0-2 xfce4-settings

Other relative issues:

Xfce sensors plugin starts with error that is cannot execute hddtemp

On Debian xcfe4-sensors-plugin is compiled without netcat feature, hence cannot read temperature information from socket. The solution suggested in documentation (/usr/share/doc/xfce4-sensors-plugin/README.Debian) is to set UID flag on hddtemp by running dpkg-reconfigure hddtemp.

Relevant links:

Installation of Plex media server

:HELP: If occasionally you have enabled required secure connections while not completing SSL setup (and have lost connection to the server), you can revert the setting by modifying the configuration file /var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Preferences.xml and setting secureConnections=1 (check here for all options).

:HELP: Log files are located in /var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Logs.

See also:

Audio

How to save master sound level for ALSA?

Usually is saved and restored during the startup/shutdown (check e.g. /etc/init.d/alsa-utils). To do it manually, do the following:

alsactl –file /var/lib/alsa/asound.state store

See Howto save AlsaMixer settings.

How set a default sound card for ALSA?

  • List cards via aplay -L
  • Test card/devices using 
    $ for i in 3 7 8 9 10; do echo "[hw:0,$i]"; speaker-test -D hw:0,$i -l1 -c2; sleep 5s; done
// Successful detection:
Playback device is hw:0,7
Stream parameters are 48000Hz, S16_LE, 2 channels
...
 0 - Front Left
 1 - Front Right
// Unsuccessful detection:
Playback device is hw:0,8
Stream parameters are 48000Hz, S16_LE, 2 channels
...
 0 - Unknown
 1 - Unknown
  • Create ~/.asoundrc or /etc/asound.conf: 
    # cat <<EOF > /etc/asound.conf
defaults.pcm.card 0
defaults.pcm.device 7
EOF

See also:

Devices and filesystems

md-RAID

Drive setup for software RAID

(sources (44 KiB, 746 downloads))

Bad block support:

A manual check can be triggered via:

  • echo check > /sys/block/mdX/md/sync_action
  • checkarray -a /dev/mdX

Usually this operation is scheduled via cron (e.g. runs on first Sunday of each month). The status and progress can be checked as following: 

# cat /proc/mdstat

Personalities : [raid6] [raid5] [raid4] [raid1]
md0 : active raid1 sdb1[0] sdc1[1]
      3906778112 blocks super 1.2 [2/2] [UU]
      [>....................]  check =  4.0% (158288320/3906778112) finish=386.5min speed=161604K/sec
      bitmap: 0/30 pages [0KB], 65536KB chunk

The check operation scans the drives for bad sectors and automatically repairs them. If while reading, a read error occurs, the check will trigger the normal response to read errors which is to generate the “correct” data and try to write that out – so it is possible that a check will trigger a write. However in the absence of read errors it is read-only.

When the check is complete, one may check how many blocks (if any) have been flagged as bad (cat /sys/block/mdX/md/mismatch_cnt). mismatch_cnt is the number of unsynchronized blocks in the RAID.

The repair is to rebuild the RAID (echo repair >/sys/block/mdX/md/sync_action) which does not reset the count, but if you force a check after the rebuild is complete, then the count should return to zero.

:HELP: Unconfirmed that repair is needed on modern kernels.

Kernel 3.1: Bad block management Write error will not fail the drive but will record the location of the write error log. Kernel will use that bad block log to record failed blocks rather than failing the whole device. After a re-assembly (e.g. when you boot up after fixing your power, cable, controller issues) md will try writing to bad blocks again, until any such writes fail, after which it will stop trying to write to bad blocks on that device. By this method, md can automatically recover from spurious write failures caused by temporary issues.

Kernel 3.7: Support for TRIM operations for the underlying SSD

Btrfs

Corruption detection and correction capabilities of btrfs

  • Can btrfs ignore bad blocks as they are discovered?
    No, it is not keeping track of bad blocks.
  • If the drive does not successfully resolve the bad block issue and btrfs takes a write failure every time it attempts to overwrite the bad data, it is not going to remap that data, but rather it is going to fail the drive?

    If the drive doesn't resolve a bad block on write, then the drive is toast. That's how md handles it. That's even how manufacturers handle it. The point at which write failures occur mean there are no reserve sectors left, or the head itself is having problems writing data to even good sectors. Either way, the drive isn't reliable for rw purposes and coming up with a bunch of code to fix bad drives isn't worth development time in my opinion.

  • How does btrfs handle bad blocks in RAID-1?

    If a block is read and fails its checksum, then the other copy (in RAID-1) is checked and used if it's good. The bad copy is overwritten with good data e.g. BTRFS error (device sda1): fixed up error at logical 92686401536 on dev /dev/sdb1 appears in kernel log. If the block is bad such that writing to it won't fix it (the drive returns an IO error) btrfs will complain in kernel log e.g. BTRFS error (device sda1): bdev /dev/sdb1 errs: wr 47, rd 0, flush 1, corrupt 0, gen 0.

  • Is running btrfs on top of LVM quite as efficient as btrfs by itself?

    LVM is like md RAID in that regard – no checksums, leaving the software entirely at the mercy of the hardware's ability to detect and properly report failure.

    In fact, it's exactly as bad as that, since while both lvm and md offer N-way-mirroring, they generally only fetch a single unchecksummed copy from whatever mirror they happen to choose to request it from, and use whatever they get without even a comparison against the other copies to see if they match or majority vote on which is the valid copy if something doesn't match. The only way they know there's an error (unless the hardware reports one) at all is if a deliberate scrub is done.

    And the RAID-5/6 parity-checking isn't any better, as while those parities are written, they're never checked or otherwise actually used except in recovery. Normal read operation is just like RAID-0; only the device(s) containing the data itself is(are) read, no parity/checksum checking at all, even the trouble was taken to calculate and write it out. When I had md RAID-6 deployed and realized that, I switched back to RAID-1 (which would have been RAID-10 on a larger system), because while I considered the RAID-6 performance costs worth it for parity checking, they most definitely weren't once I realized all those calculates and writes were for nothing unless an actual device died, and RAID-1 gave me that level of protection at far better performance.

    Btrfs will not return corrupted data unless CoW is disabled (noCoW turns of checksumming only for data, i.e. metadata is always checksummed). However btrfs will also not repair the “bad” copy – use btrfs scrub for that.

  • CoW, checksumming and consistency

    If the file is CoW'd and checksummed, and there's a crash, there is supposed to be consistency: either the old state or new state for the data is on-disk and the current valid metadata correctly describes which state that data is in.

    If the file is not CoW'd and not checksummed, its consistency is unknown but also ignored when doing normal reads, balance or scrubs.

    If the file is not CoW'd but were checksummed, there would always be some inconsistency if the file is actively being modified. Only when it's not being modified, and metadata writes for that file are committed to disk and the superblock updated, is there consistency. At any other time, there's inconsistency. So if there's a crash, a balance or scrub or normal read will say the file is corrupt. And the normal way Btrfs deals with corruption on reads from a mounted fs is to complain and it does not pass the corrupt data to user space, instead there's an i/o error. You have to use restore to scrape it off the volume; or alternatively use btrfsck to recompute checksums.

  • RAID-Z and dynamic stripe width

    RAID-5 (and other data/parity schemes such as RAID-4, RAID-6, even-odd, and Row Diagonal Parity) never quite delivered on the RAID promise – and can't – due to a fatal flaw known as the RAID-5 write hole. Whenever you update the data in a RAID stripe you must also update the parity, so that all disks XOR to zero – it's that equation that allows you to reconstruct data when a disk fails. The problem is that there's no way to update two or more disks atomically, so RAID stripes can become damaged during a crash or power outage.

    To see this, suppose you lose power after writing a data block but before writing the corresponding parity block. Now the data and parity for that stripe are inconsistent, and they'll remain inconsistent forever (unless you happen to overwrite the old data with a full-stripe write at some point). Therefore, if a disk fails, the RAID reconstruction process will generate garbage the next time you read any block on that stripe. What's worse, it will do so silently – it has no idea that it's giving you corrupt data.

    There's also a nasty performance problem with existing RAID schemes. When you do a partial-stripe write – that is, when you update less data than a single RAID stripe contains – the RAID system must read the old data and parity in order to compute the new parity. That's a huge performance hit. Where a full-stripe write can simply issue all the writes asynchronously, a partial-stripe write must do synchronous reads before it can even start the writes.

btrfs on flash/USB devices

  • btrfs on flash/USB devices:

    CoW designs tend naturally to work well with flash media. F2FS is specifically designed to work well with flash, whereas for btrfs it is a natural consequence of the copy-on-write design. With both filesystems, if you randomly generate a 1GB file and delete it 1000 times, onto a 1TB flash, you are very likely to get exactly one write to every block on the flash (possibly two writes to <1% of the blocks) rather than, as would be the case with non-CoW filesystems like FAT, 1000 writes to a small chunk of blocks.

  • USB drives:

    There's several possibilities for failure, including flaky connections (sometimes assisted by cats or kids), unstable USB host port drivers, and unstable USB/ATA translators. A number of folks have reported problems with such filesystems with devices connected over USB, that simply disappear if they direct-connect the exact same devices to a proper SATA port. The problem seems to be /dramatically/ worse with USB connected devices, than it is with, for instance, PCIe-based SATA expansion cards.

Replacing failing device

If device is failing (e.g. there are write/flush errors), it can be replaced by one of the methods:

So in summary, without temporarily adding an additional drive, there are 3 ways to replace a drive (see Replacing drives with larger ones in a 4 drive raid1):

  1. Logically removing old drive (triggers 1st rebalance), physically removing it, then adding new drive physically and logically (triggers 2nd rebalance).
  2. Physically removing old drive, mounting degraded, logically removing it (triggers 1st rebalance, while degraded), then adding new drive physically and logically (2nd rebalance).
  3. Physically replacing old with new drive, mounting degraded, then logically replacing old with new drive (triggers rebalance while degraded).

From here and here:

There is a feature request to tell btrfs to store metadata on external SSD/USB drive for speedup. Another alternative is combination of Bcache+btrfs.

Shrink btrfs partition

btrfs dev resize to shrink it to (slightly smaller than) the replacement device, then btrfs replace should work. Then btrfs dev resize max to fill up the replacement device completely.

How to convert RAID1 volume into single-drive volume

In below example /dev/sdb is failing drive which we want to remove, and remaining /dev/sda should be converted into single-drive volume:
  • Detach failing drive or run echo 1 > /sys/block/sdb/device/delete (check here for more information)
  • Mount healthy device in degraded mode: mount /dev/sda /mnt/tmp -o degraded
  • Convert from RAID1 to RAID0: btrfs balance start -f -mconvert=single -dconvert=single /mnt/tmp
  • Remove detached drive from btrfs volume: btrfs device remove missing /mnt/tmp

btrfs device delete /dev/sdc1 /mnt/raid1 user experience

In order to recover from single drive failure in raid1 volume the healthy drive can be separately mounted with -o degraded and you can re-establish two copy replication with btrfs dev add with a new drive and btrfs dev del missing to get rid of the phantom missing drive.

A gotcha with this technique though is often single chunks get created during the -o degraded read-write mount. After dev del missing completes the replication process, you need to check btrfs fi df or btrfs fi us for single chunks. If they exist, get rid of them with a filtered balance: btrfs balance -dconvert=raid1,soft -mconvert=raid1,soft should work I think. If there are single chunks created and not converted, later if you need to do a degraded mount it will fail. Usually it can be made to work with -o ro,degraded in such a case, but it means no more read-write for the file system and you'd have to recreate it.

btrfs corruption when devices are missing for kernels before 4.3

It is not possible to use a volume in degraded mode if RAID0 has been used for data and the device had not been properly removed with btrfs device delete (some stripes will be missing). The situation is even worse if RAID0 is used for the the metadata: trying to mount a BTRFS volume in read/write mode while not all the devices are accessible will simply kill the remaining metadata, hence making the BTRFS volume totally unusable… you have been warned!

:HELP: This is not actually true, but the bug is better explained here and there:

Loss of one device of a two-device raid1 (in case mounting degraded writable) will force new chunks to be written in single mode, because there's not a second device to write to (so writing raid1 is no longer possible). So far, so good. But then on an unmount and attempt to mount again, btrfs sees single mode chunks on a two-device btrfs, and knows that single mode normally won't allow a missing device, so forces read-only, thus blocking adding a new device and rebalancing all the single chunks back to raid1. The fix will be in first Linux kernel 4.3 release.

btrfs corruption due to partition cloning / UUID collision

Because btrfs can be multi-device, it needs some way to track which devices belong to each filesystem, and it uses filesystem UUID for this purpose.

If you clone a filesystem (for instance using dd or lvm snapshotting, doesn't matter how) and then trigger a btrfs device scan, say by plugging in some other device with btrfs on it so udev triggers a scan, and the kernel sees multiple devices with the same filesystem UUID as a result, and one of those happens to be mounted, you can corrupt both copies as the kernel btrfs won't be able to tell them apart and may write updates to the wrong one.

Prevention: Don't let btrfs see both copies at the same time. If you need to clone the filesystem, ideally make sure it's unmounted at the time, and detach either the original device or the clone immediately upon finishing the clone operation (before doing anything that might trigger a btrfs device scan, including device plugging that would trigger udev to trigger such a scan). Then simply keep them separate, only attaching one at a time and definitely never mounting the filesystem with both the clone and the original devices attached, so the kernel can't get confused and write to the wrong one because the other one is never there at the same time to provide the opportunity.

Cannot balance FS (No space left on device)

What a balance does is to send everything selected by the filters through the allocator again, and specifically prevent any existing chunks from being used to satisfy the allocation. When you have 5 data chunks that are 20% used and run balance -dlimit=20, it doesn't pack that all into the first chunk, it allocates a new chunk, and then packs it all into that, then frees all the other chunks. This behaviour is actually a pretty important property when adding or removing devices or converting between profiles, because it's what forces things into the new configuration of the filesystem.

In an ideal situation, the limit filters should make it repack into existing chunks when specified alone, but currently that's not how it works, and I kind of doubt that that will ever be how it works.

Allocation policy

If you're using a non-striped RAID level (single, 1), btrfs will start by filling up the largest devices first: balance attempts to make the free space equal across the devices, not to make the used space equal.

If you're using a striped RAID level (0, 5, 6), then btrfs will fill up the devices equally, until one is full, and then switch to using the remaining devices (until one is full, etc).

Data read load balancing

btrfs chooses which copy of the two will be read very simply, based on the PID making the request. Odd PIDs get assigned one copy, even PIDs the other.

defrag after dedup

Explicit defrag always undoes dedup, so you never want to defrag a file after dedup has removed duplicate extents from it.

Defrag before dedup is a more complex situation that depends on the dedup strategy of whichever dedup tool you are using:

  • A file-based dedup tool doesn't have to care about extent boundaries, so you can just run defrag and then dedup – in that order.
  • An extent-based dedup tool will become less efficient after defrag and some capabilities will be lost, e.g. it will not be able to dedup data between VM image files or other files on the host filesystem. Extents with identical content but different boundaries cannot be deduped. There are fewer opportunities to find duplicate extents because defrag combines smaller extents into bigger ones.
  • A block-based dedup tool explicitly arranges the data into extents by content, so extents become entirely duplicate or entirely unique. This is different from what defrag does. If both are run on the same data they will disagree on physical data layout and constantly undo each other's work.

When data is defragged, it appears in find-new output as “new” data (the same as if the data had been written to a file the usual way). An incremental dedup tool that integrates defrag and find-new at the same time has to carefully prevent itself from consuming its own output in an endless feedback loop.

shapshots influence on defrag

However, be aware that if you have snapshots locking down the old extents in their fragmented form, a manual defrag will copy the data to new extents without releasing the old ones as they're locked in place by the snapshots, thus using additional space. Worse, if the filesystem is already heavily fragmented and snapshots are locking most of those fragments in place, defrag likely won't help a lot, because the free space as well will be heavily fragmented. So starting off with a clean and new filesystem and using autodefrag from the beginning really is your best bet.

btrfs zone types

From here:

In btrfs, there's four types of allocations aka “zones”:
  1. Unallocated (unzoned)
    Can be used for anything but must be allocated/zoned first
  2. System
    Critical but limited in size and generally only allocated at mkfs or when adding a new device.
  3. Data
    The actual file storage, generally the largest allocation.
  4. Metadata
    Information about the files: where they are located (the location and size of individual extents), ownership and permissions, date stamps, checksums, and for very small files (a few KiB), sometimes the file content itself.
    • Global reserve
      A small part of metadata reserved for emergency use only. Btrfs is pretty strict about its use, and will generally error out with ENOSPC if metadata space other than the global reserve is used up, before actually using this global reserve. As a result, any of the global reserve used at all indicates a filesystem in very severe straits, crisis mode.

Btrfs in practice tends to be a bit liberal about allocating/zoning data chunks, since it's easier to find bigger blocks of space in unallocated space than it is in busy partly used data space. Over time, therefore, more and more space tends to be allocated to data, while existing data space, like those blocks near city center, may have most of its files/buildings deleted, but still have a couple still occupied.

From here:

With mixed mode, data and metadata are mixed in the same chunks (it's still very strongly recommended for filesystems under 1 GiB, and recommended in general between 8 and 32 GiB), and balance will refuse to run with balance filters unless the -d and -m filters exactly duplicate each other (balance -dusage=50 -musage=50). Otherwise invoking balance with both an -musage and a -dusage filter is rare except the examples dealing with specific cases where metadata or data (usually metadata), has run out, due to the other one (data), taking all the unallocated space with mostly empty allocations. So a quick -dusage filter to clear out the mostly empty data allocations is the most common example seen.

More information:

How to map btrfs logical sector to physical sector?

Example:

[17606.989497] BTRFS error (device sdb1): unable to fixup (regular) error at logical 3037444042752 on dev /dev/sdc1 

# btrfs-map-logical -l 3037444042752 /dev/sdc1
mirror 1 logical 3037444042752 physical 2554240299008 device /dev/sdc1
...
# dd if=/dev/sdc1 bs=4096 skip=2554240299008 count=1 of=block_sdc1

Is there a way to map inodes to paths?

btrfs inspect-internal inode-resolve <inode> <volume>

This resolves the <inode> in subvol <volume> to its fs paths

I've got some bad blocks on partition. How can I fix it?

In my logs there is stated:

/var/log/syslog

kernel: sd 2:0:0:0: [sda] Unhandled sense code
kernel: sd 2:0:0:0: [sda] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
kernel: sd 2:0:0:0: [sda] Sense Key : Medium Error [current] [descriptor]
kernel: Descriptor sense data with sense descriptors (in hex):
kernel:         72 03 11 04 00 00 00 0c 00 0a 80 00 00 00 00 00
kernel:         01 58 f6 f9
kernel: sd 2:0:0:0: [sda] Add. Sense: Unrecovered read error - auto reallocate failed
kernel: sd 2:0:0:0: [sda] CDB: Read(10): 28 00 01 58 f6 f8 00 00 08 00

and smartd daemon reports: 

Device: /dev/sda [SAT], 1 Currently unreadable (pending) sectors

The above means that the bad block was found, but HDD failed to reallocate it automatically.

The legal approach is to dump the whole FS somewhere, run badblocks8) utility on the given partition and reformat it (will work for e.g. EXT3). Unfortunately, mkfs.xfs (and mkfs.reiserfs) does not take any list of bad blocks which can be fed from badblocks and XSF does not support list of bad blocks as well.

First what you can try, is to read all files from filesystem (e.g. tar -c / -O > /dev/null or find / -type f -exec cp '{}' /dev/null \; or genisoimage -D -r -udf -allow-limited-size / > /dev/null) and see what files are failed to read. Then you need to nullify this file, e.g. via dd if=/dev/zero of=/bad/file bs=1 count=<file_size>. If the faulty file was not found then follow the steps described in Bad block HOWTO. In two words: you need to find out the number of the block (using e.g. dd) that fails, move (or remove) the file that contains this block, to different place and nullify the block. After that HDD will notice that block is ready for re-allocation and replacement with another block from a pool for such cases.

Another solution could be to create partitions so that bad blocks do not belong to partitioned areas (see Как удалось оживить битый HDD для хранения чего-нибудь ненужного) and join them using mdadm or LVM or btrfs.

Additional links:

Ext4-fs reports corruption problems

Exts4 filesystem driver started reporting unusual messages: 
EXT4-fs error (device sda3): ext4_ext_check_inode:481: inode #4857903: comm updatedb.mlocat: pblk 0 bad header/extent: too large eh_max - magic f30a, entries 1, max 1540(4), depth 0(0)
EXT4-fs error (device sda3): ext4_ext_check_inode:481: inode #4724129: comm tar: pblk 0 bad header/extent: invalid extent entries - magic f30a, entries 1, max 4(4), depth 1(1)
EXT4-fs error (device sda4): ext4_mb_generate_buddy:756: group 162, 27838 clusters in bitmap, 27848 in gd; block bitmap corrupt.
EXT4-fs (sda4): Inode 1574118 (ede4e380): orphan list check failed!
EXT4-fs error (device sda2): htree_dirblock_to_tree:920: inode #264418: block 1057309: comm find: bad entry in directory: rec_len % 4 != 0 - offset=524(524), inode=18087964, rec_len=28781, name_len=116
EXT4-fs (sda2): Remounting filesystem read-only

After some time, partition(s) are re-mounted read-only and system operation shortly stops.

EXT4-fs error, kernel BUG says:

Common cause of this is the block address getting corrupted, so that the hard drive read the correct data from the wrong location.

but it turned out to be the problem with one of the memory bank which was corrupting the data (and by co-incidence allocated for disk buffers). As overview:

  • If problem occurs on different partitions or drives but S.M.A.R.T. indicators are not going worth, then it is a signal that problem is not connected with hard drive damage.
  • If filesystem repair is started (e.g. fsck /dev/sda2), it reports about corrupted directory entries, orphan free blocks (and so on), it fixes the problems and you immediately re-run fsck and it finds the same sort of problems again, then the corruption happens either when data is transferred to hard drive or back from it.

… it's time to run memtest which will anyway not harm, but will save you many hours trying to find a problem in hard drive or cables or controller.

How to force OS to check given filesystem on startup?

Add fsck.mode=force to kernel parameters (for example, edit /etc/default/grub, modify GRUB_CMDLINE_LINUX_DEFAULT and run update-grub). :OPT: Use fsck.repair=preen to automatically fix what can be safely fixed.

See also Fsck in relation to how tune ext2/3/4 filesystems to be checked after certain amount of time or mounts.

:DEL: How to force OS to check given filesystem on startup?:

  • Run touch forcefsck in the root directory of the mounted filesystem. This file will be removed after filesystem is checked at boot.
  • Add forcefsck to kernel options. This will force check for all filesystems to be mounted at boot.

How to mount XFS filesystem with extended file attributes support?

Do not know yet. Similar problems: here, here, here

How to use video RAM as block device

Check Using Graphics Card Memory as Swap (wiki archive version has a bit more information). However in practice the speed is 1-5 MBps, which is x4 times slower then HDD. Also:

Unlike motherboard RAM and hard drives, there aren't any known video cards that have ECC memory. This may not be a big deal for graphics rendering, but you definitely don't want to put critical data in it or use this feature on servers.

Example of allocating 123MB (0x7b00000) vRAM with 1280×1024 32bit display (check fbset output): 

# lspci -vvv | less
01:05.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] RS690M [Radeon Xpress 1200/1250/1270] [1002:791f] (prog-if 00 [VGA controller])
        Subsystem: Toshiba America Info Systems RS690M [Radeon Xpress 1200/1250/1270] [1179:ff1a]
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 64, Cache Line Size: 32 bytes
        Interrupt: pin A routed to IRQ 18
        NUMA node: 0
        Region 0: Memory at f0000000 (64-bit, prefetchable) [size=128M]
        Region 2: Memory at f8100000 (64-bit, non-prefetchable) [size=64K]
        Region 4: I/O ports at 9000 [size=256]
        Region 5: Memory at f8000000 (32-bit, non-prefetchable) [size=1M]
        [virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
        Capabilities: [50] Power Management version 2
                Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
                Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
        Capabilities: [80] MSI: Enable- Count=1/1 Maskable- 64bit+
                Address: 0000000000000000  Data: 0000
        Kernel driver in use: radeon
        Kernel modules: radeon
# modprobe slram map=VRAM,0xf0500000,+0x7b00000     # 1280*1024*4 = 0x500000 → 0xf0500000,+0x7b00000
# modprobe mtdblock
# hdparm -t /dev/mtdblock0

/dev/mtdblock0:
 Timing buffered disk reads:  48 MB in  3.10 seconds =  15.49 MB/sec

Using compressed in-memory drives

:INFO: One can install zram-tools (which installs zramswap.service) and modify /etc/default/zramswap as needed, however unfortunately this package only focuses on swap, i.e. it is cumbersome to tune other zram partitions for other needs.

More flexible is the following approach:

  • Enable zram module and tune it for 2 devices: 
    # cat > /etc/modules-load.d/zram-drive.conf <<'EOF'
zram
EOF
# cat > /etc/modprobe.d/zram-drive.conf <<'EOF'
options zram num_devices=2
EOF
  • Run modprobe zram and check that devices have been created: 
    # ls -l /dev/zram*
brw-rw---- 1 root disk 254, 0 Dec 29 22:56 /dev/zram0
brw-rw---- 1 root disk 254, 1 Dec 29 22:56 /dev/zram1
  • Make use of zram-setup@.service from udisks2 package. This service reads settings from /usr/local/lib/zram.conf.d/%i-env by default (where %i is substituted by device name e.g. zram0) but it can be tuned as following: 
    # cat > /etc/systemd/system/zram-setup@.service <<'EOF'
#
# Service initializes zram devices
#
[Unit]
Description=Setup zram based device %i
Requires=dev-%i.device
After=dev-%i.device
Before=local-fs.target

[Service]
Type=oneshot
RemainAfterExit=yes
EnvironmentFile=-/etc/zram.conf.d/%i
ExecStart=/bin/sh -c 'if [ -n "$ZRAM_COMPRESSION" ]; then echo $ZRAM_COMPRESSION > /sys/class/block/%i/comp_algorithm; fi'
ExecStart=/bin/sh -c 'if [ -n "$ZRAM_STREAMS_NUM" ]; then echo $ZRAM_STREAMS_NUM > /sys/class/block/%i/max_comp_streams; fi'
ExecStart=/bin/sh -c 'if [ -n "$ZRAM_DEV_SIZE" ];    then echo $ZRAM_DEV_SIZE    > /sys/class/block/%i/disksize; fi'
ExecStart=/bin/sh -c 'if [ "$SWAP" = "y" ];          then mkswap /dev/%i && swapon /dev/%i; fi'
ExecStart=/bin/sh -c 'if [ "$MKE2FS" = "y" ];        then mke2fs -q -m 0 -b 4096 -O sparse_super -L %i /dev/%i && mount -t ext2 /dev/%i /tmp && chmod 1777 /tmp; fi'
ExecStop=-/bin/sh -c 'echo 1 > /sys/class/block/%i/reset'

[Install]
WantedBy=local-fs.target
EOF
# cat > /etc/zram.conf.d/zram0 <<'EOF'
ZRAM_COMPRESSION=lz4
ZRAM_DEV_SIZE=100M
SWAP=y
EOF
# cat > /etc/zram.conf.d/zram1 <<'EOF'
ZRAM_COMPRESSION=lz4
ZRAM_DEV_SIZE=100M
MKE2FS=y
EOF
# systemctl daemon-reload
# systemctl enable zram-setup@zram0.service
# systemctl enable zram-setup@zram1.service
  • Make sure that swap partition is active and /tmp is mounted: 
     # swapon
NAME       TYPE      SIZE USED PRIO
/dev/zram0 partition 100M 100M   -2

# systemctl status tmp.mount
* tmp.mount - /tmp
   Loaded: loaded
   Active: active (mounted) since Sat 2020-10-03 01:44:10 CEST; 3 months 4 days ago
    Where: /tmp
     What: /dev/zram1
    Tasks: 0 (limit: 4915)
   Memory: 0B
   CGroup: /system.slice/tmp.mount

:WARN: In above approach there is a need to mount /tmp just because it should be set 1777 permission afterwards. Unfortunately there is no “mode=1777” mount option for ext2 (as for tmpfs) otherwise it would be possible to leverage mounting step to /etc/fatab.

See also:

Renaming a file on Samba share does not always correspond to Linux ideology

It is not possible to rename/move a read-only file on Samba share, even if it the containing directory is writeable.

The easiest way is to disable DOS-to-UNIX attributes mapping (read here in details):
map readonly = no
map archive = no
map system = no
map hidden = no

Another possible variants is to use store dos attributes = yes and delete readonly = yes.

Map Windows user to Unix user

  • Create new TDB using tdbtool dummy.tdb create /var/lib/samba/winbindd_idmap.tdb
  • Add idmap config * : tdb to /etc/samba/smb.conf

To get list of cashed SID↔UID mappings: 

# net cache list | grep S-1-5-21
Key: IDMAP/SID2XID/S-1-5-21-2724446181-3664060749-2626026913-3000        Timeout: Sun Jul 22 20:53:17 2010       Value: 1000:U
Key: IDMAP/UID2SID/1000  Timeout: Sun Jul 22 20:53:17 2010       Value: S-1-5-21-2724446181-3664060749-2626026913-3000
Key: IDMAP/SID2XID/S-1-5-21-2724446181-3664060749-2626026913-501         Timeout: Sun Jul 22 23:17:17 2010       Value: 65534:U
Key: IDMAP/UID2SID/65534         Timeout: Sun Jul 22 23:17:17 2010       Value: S-1-5-21-2724446181-3664060749-2626026913-501

To get local SID: 

# net getlocalsid
SID for domain HOMENET is: S-1-5-21-2724446181-3664060749-2626026913

To list all Samba users (either from smbpasswd or LDAP – specified by passdb backend option in smb.conf): 

# pdbedit -L -v
Unix username:        backup
NT username:          backup
Account Flags:        [U          ]
User SID:             S-1-5-21-2724446181-3664060749-2626026913-3000
Primary Group SID:    S-1-5-21-2724446181-3664060749-2626026913-513
Full Name:            Backup User
Home Directory:       \\homenet\backup
HomeDir Drive:
Logon Script:
Profile Path:         \\homenet\backup\profile
Domain:               HOMENET
Account desc:
Workstations:
Munged dial:
Logon time:           0
Logoff time:          never
Kickoff time:         never
Password last set:    Sun, 12 Jul 2015 12:58:25 CEST
Password can change:  Sun, 12 Jul 2015 12:58:25 CEST
Password must change: never
Last bad password   : 0
Bad password count  : 0
Logon hours         : FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

To change SID for the given user: 

# pdbedit --user backup -U S-1-5-21-2724446181-3664060749-2626026913-3001
smbldap_search_domain_info: Searching for:[(&(objectClass=sambaDomain)(sambaDomainName=HOMENET))]
smbldap_open_connection: connection opened
init_sam_from_ldap: Entry found for user: backup
init_ldap_from_sam: Setting entry for user: backup
ldapsam_update_sam_account: successfully modified uid = backup in the LDAP database

To get user→SID mapping from winbind (either from Samba user DB or as specified by idmap config option in smb.conf): 

$ wbinfo -n '\backup'
S-1-5-21-2724446181-3664060749-2626026913-3000 SID_USER (1)

To get SID→user mapping from winbind: 

$ wbinfo --lookup-sids S-1-5-21-2724446181-3664060749-2626026913-3000
S-1-5-21-2724446181-3664060749-2626026913-3000 -> <none>\backup 1

To get user→SID mapping on Windows: 

C:\> wmic useraccount get name,sid
Name           SID
Administrator  S-1-5-21-1827375663-6890924511-1272660413-500
User           S-1-5-21-1827375663-6890924511-1272660413-1000

See also:

How to list the content of remote share?

smbclient //server/share -c ls

How to configure HDD to spin-off after certain inactivity time?

Add the corresponding section to /etc/hdparm.conf. The options from that section are applied to corresponding drive once it is attached to the system:

/etc/hdparm.conf

/dev/disk/by-uuid/91e32677-0656-45b8-bcf5-14acce39d9c2 {
    spindown_time = 240
}

How to mark USB flash as non-rotating device?

Linux is not able to detect non-rotating devices (like flash sticks) and hence cannot apply certain optimizations

First step is to find out the way how to identify your flash stick, for example, using ID. For that inspect /dev/disk/by-id directory or lsusb output.

/etc/udev/rules.d/90-non-rotational.rules

# Mark given USB devices as non-rotational:
ACTION=="add|change", SUBSYSTEMS=="usb", ENV{ID_SERIAL}=="SanDisk_Ultra_Fit_*-0:0", ATTR{queue/rotational}="0", ATTR{queue/scheduler}="deadline"

# Change scheduler for SSD drives:
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="deadline"

To list all properties of the given drive use udevadm info -q all -n /dev/sda.

See also SSD optimization.

USB device is reporting usb 1-2: reset high speed USB device using ehci_hcd and address 2

General advices:
  • Check/change the USB cable
  • Try another USB port
  • Try to reduce the number of sectors to read/write to device (see Linux USB FAQ):
    echo 16 > /sys/block/sdb/device/max_sectors
  • Disable ehci_hcd module (this will downgrade USB from 2.0 to 1.1 thus reduce disk performance in times):
    echo "blacklist ehci_hcd" >> /etc/modprobe.d/blacklist.conf

Further reading:

Posted by me:

What would be the performance impact if module uhci_hcd is used instead of ehci_hcd?

The performance drops down in 30 times:
# hdparm -tT /dev/sdb

/dev/sdb:
 Timing cached reads:       2464 MB in  2.00 seconds = 1232.46 MB/sec
 Timing buffered disk reads:  92 MB in  3.04 seconds = 30.27 MB/sec

# rmmod ehci_hcd
[   72.848048] ehci_hcd 0000:00:1d.7: USB bus 1 deregistered
[   72.850412] ehci_hcd 0000:00:1d.7: PCI INT A disabled
[   73.084041] usb 2-1: new full-speed USB device number 2 using uhci_hcd
[   73.332925] usb 2-1: New USB device found, idVendor=1058, idProduct=1104
[   73.335280] usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[   73.337638] usb 2-1: Product: My Book
[   73.339936] usb 2-1: Manufacturer: Western Digital
[   73.342251] usb 2-1: SerialNumber: 575532553130303530353538
[   73.397554] scsi5 : usb-storage 2-1:1.0
[   73.479146] input: Western Digital My Book as /devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1:1.1/input/input4
[   73.482549] generic-usb 0003:1058:1104.0002: input,hidraw0: USB HID v1.11 Device [Western Digital My Book] on usb-0000:00:

# hdparm -tT /dev/sdb

/dev/sdb:
 Timing cached reads:          2 MB in  2.01 seconds = 1016.81 kB/sec
 Timing buffered disk reads:   4 MB in  4.05 seconds = 1011.35 kB/sec
  • uhci_hcd is USB Universal Host Controller Interface driver
  • ehci_hcd is USB 2.0 'Enhanced' Host Controller (EHCI) driver
  • xhci_hcd is USB 3.0 eXtensible Host Controller Interface (xHCI) driver

To check what module is used to access a specific, examine lsusb -tv output: 

# lsusb -t
/:  Bus 05.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/8p, 480M
    |__ Port 1: Dev 2, If 0, Class=Mass Storage, Driver=usb-storage, 480M
    |__ Port 4: Dev 4, If 0, Class=Mass Storage, Driver=usb-storage, 480M
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=uhci_hcd/2p, 12M
    |__ Port 2: Dev 2, If 0, Class=Hub, Driver=hub/4p, 12M
        |__ Port 1: Dev 6, If 0, Class=Mass Storage, Driver=usb-storage, 12M

One can see that two first USB drives are connected via hi-speed interface, and third one via low-speed hub.

See also:

find . -type f -links +1 -exec ls -li '{}' \;

After one can use one of the strategies to list particular group of files (from List all files with the same inode?):

  • find -samefile /some/file
  • find -inum 12353538

How to synchronize remote file contents with local one?

The most reliable way is to use rsync:

rsync -itmz -P --checksum --inplace -e 'ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null' file.7z host:/path/file.7z

How to optimize ISO image, making files with same content point to same data?

Such patch exists within mkisofs-md5 project (check for mkisofs-md5-2.01-xxx). However cdrtools-2.01.01.a59 and earlier do not compile under Debian 6.0, see this mail thread.

The patch cdrtools-3.00-duplicates-once-with-md5c.diff.bz2 (cdrtools-3.00-duplicates-once-with-md5c.diff.bz2.asc) includes the changes necessary to be applied on the top of original source to enable support of “duplicates-once” functionality. Compile the project with make. Use like this:

mkisofs -udf -iso-level 3 -duplicates-once -o /path/to/file.iso /path/to/data

Also posted here.

In UltraISO the same option is available in File → Properties → Optimize.

In Debian the utility is available in genisoimage package.

How to create DVD ISO from VIDEO_TS directory?

Assuming that current directory contains VIDEO_TS and AUDIO_TS, the following command will create DVD ISO:

genisoimage -dvd-video -V “My disk label” -o dvdimage.iso .

SuSE

Questions answered

How to list all packages installed during the given year? 

$ rpm -qa --queryformat "%{NAME}\t%{DISTRIBUTION}\t%{INSTALLTIME:date}\n" | grep "2014$" | sort
libxfce4mcs     openSUSE 11.1   Mon Jan 13 15:56:56 2014
libxfce4util    openSUSE 11.1   Mon Jan 13 15:56:55 2014
libxfcegui4     openSUSE 11.1   Mon Jan 13 15:56:56 2014

Debian

How to configure proxy for APT?

echo 'Acquire::http::Proxy "http://centurion:3128";' > /etc/apt/apt.conf.d/99proxy

Create the following file: 
# cat > /etc/apt/apt.conf.d/01norecommend <<'EOF'
APT::Install-Recommends "0";
APT::Install-Suggests "0";
EOF

After that if you want to override the behaviour use the following:

apt-get install --install-recommends ...

How to become a Debian Maintainer

Packaging hints

  • Install the package sources using apt-get source <package>.
  • Check if the package lintian clean (lintian -i -I --show-overrides binpackage-version.deb output from lintian package). Check the description of the problem here (click on corresponding message reported).
  • Check if licenses are compatible across all sources (use licensecheck -r . from devscripts package to display all of them).
  • Test all the .deb packages with piuparts binpackage-version.deb (from piuparts package).
  • To find out what packages your package needs to be built run the command dpkg-depcheck -d ./configure, to manually find exact build dependency for /usr/bin/foo execute objdump -p /usr/bin/foo | grep NEEDED.
  • You need to specify the following in your ~/.profile: 
    # For dh_make:
export DEBEMAIL=joy-mg@debian.org DEBFULLNAME="Josip Rodin"
# For debuild:
export DEBUILD_LINTIAN_OPTS="-i -I --show-overrides"
# For debsign:
export DEBSIGN_KEYID="0x124AB157"
  • To generate a stub debian directory run dh_make --copyright gpl2 (from package dh_make).
  • dch is used to add new entries to the changelog or modify existing ones:
    • debchange --newversion X.Y to add new entry
    • debchange -a "New version 3.0" --closes 123,456 to append to top-most entry
  • To manipulate the patches use quilt utility:
    • quilt import -P local_file.patch external_file.patch
  • … or dpatch utility:
    • cat my.patch | dpatch patch-template -p "nnn_short_description" "Some human friendly description." > nnn_file.dpatch; echo "nnn_file.dpatch" >> 00list
  • To install all build dependencies use apt-get build-dep <package> (if package is not installed / prepared) or :OPT: mk-build-deps -i if package is already downloaded and prepared via dpkg-source -x package.dsc.
  • The preferable way to build a project is debuild -sa (it will run dpkg-buildpackage -rfakeroot, lintian and debsign) or :OPT: dpkg-buildpackage -b -rfakeroot -us -uc if source was not downloaded.
  • To clean the source tree run make -f debian/rules clean or debuild – clean while will run the same command.
  • To list the contents of DEB file use dpkg --contents filename.deb, and to print the specific file use dpkg --fsys-tarfile filename.deb | tar -xOf - --wildcards \*/copyright | less
  • You can run the uscan command from devscripts to check for upstream updates based on debian/watch file.
  • To upload the package use dupload -t mentors cream_1.23-1_i386.changes
  • To populate the documentation of the package to system-wide infrastructure have a look at doc-base project.
  • To modify the .deb package use dpkg-deb -R original.deb tmp; vi tmp/DEBIAN/control; dpkg-deb -b tmp fixed.deb;

Questions answered

What are /usr/lib/pkgconfig/nnn.pc files?

pkg-config file contains the information about the package version, CFLAGS and LIBS used to assemble the package. It is preferred to libtool, and .la files are in the process of being replaced by .pc files.

Additional links:

debuild fails with missing file

Compilation fails with message:

/path/to/missing: no such file or directory

Re-run autoreconf -vif

apt-get update fails with signature verification error

apt-get update fails with the following error: 
W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used.
GPG error: http://ftp.nl.debian.org sid InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553
W: Failed to fetch http://ftp.nl.debian.org/debian/dists/sid/InRelease

Import the new repository key using the command (check that archive-key-7.0.asc is actually the latest one):
wget -q http://ftp-master.debian.org/keys/archive-key-7.0.asc -O- | sudo apt-key add -

See also Force update from unsigned repository.

apt-get update fails with The method driver /usr/lib/apt/methods/http could not be found

Do apt-get install apt-transport-https

apt-get update fails with E: Repository '…' changed its 'Origin' value from '…' to '…'

From Explicitly accept change for PPA 'Label':

Do apt-get update –allow-releaseinfo-change

How to reinstall already installed package?

apt-get install --reinstall package1 ...

How to mark manually installed package as 'auto'?

To undo this mark use apt-mark: 
# apt-get install libphp-adodb
libphp-adodb is already the newest version (5.20.4-1).
libphp-adodb set to manually installed.

# apt-mark auto libphp-adodb
libphp-adodb was set to automatically installed.

How to install a particular version of the package via apt-get (downgrade)?

apt-get install wine=1.6.2-20 wine32=1.6.2-20 libwine=1.6.2-20

After that it is advised to prevent auto updating the package to the newer version:

for package in wine wine32 libwine; do echo "$package hold" | dpkg --set-selections; done

:OPT: apt-mark hold $package

Remind yourself which packages are on hold:

dpkg --get-selections | egrep 'hold$'

:OPT: apt-mark showhold

To unhold the package run:

echo "$package unhold" | dpkg --set-selections

:OPT: apt-mark unhold $package

More radically one can uninstall packages with dpkg -r --force-depends ... and install them from DEB.

How to install some local DEB package with dependencies from repository?

  • Download DEB file(s) (if necessary) e.g. via apt-get download my.deb
  • :OPT: Install it via dpkg -i my.deb and install all dependencies via apt-get install -f
  • :OPT: Install it via apt-get install my.deb

How to output Debian dependency tree to terminal?

apt-rdepends-tree.sh outputs dependencies up to 2nd level.

How to ignore the post-install scripts for DEB package?

Remove (or copy to another place) the postinst file:

rm /var/lib/dpkg/info/<package>.postinst

How to list packages by installation date?

ls -lt /var/lib/dpkg/info/ | grep .list

How to verify files from installed packages?

Install debsums and run debsums -ca.

How to find out half-configured/broken packages?

dpkg-query -f '${status} ${package}\n' -W | grep “half-configured” or dpkg –audit.

How to recompile Debian kernel?

You will need 10GB of disk space for below procedure (pre-requisites, compilation and resulting packages).

  • Download & unpack kernel:
    $ apt-get source linux-image-3.2.0-4-686-pae; cd linux-3.2.35
    or if you have all prerequisites downloaded:
    $ dpkg-source -x linux_3.2.41-4.dsc; cd linux-3.2.35
  • [obsolete] Modify debian/config/defines so that ABI is different. Do not simply increase the number: you may collide with future official kernel release.

    debian/config/defines

    --- debian/config/defines.orig  2013-04-23 18:44:09.560859905 +0200
+++ debian/config/defines       2013-04-23 18:43:42.772860608 +0200
@@ -1,5 +1,5 @@
 [abi]
-abiname: 4
+abiname: 4fix
 ignore-changes:
  module:net/l2tp/*
 # A bunch of NFS/SunRPC exports, not selected by module because MIPS has
  • :OPT: If you want to play with kernel config then first prepare the source tree:
    $ fakeroot debian/rules source
    $ fakeroot make -f debian/rules.gen setup_i386_none_686-pae
    • If you have ready-to-use .config file, copy it to kernel source tree:
      $ cp /boot/config-3.2.0-4-686-pae debian/build/build_i386_none_686-pae/.config
    • If you want to configure the kernel, run:
      $ make -C debian/build/build_i386_none_686-pae menuconfig
  • Now run compilation:
    $ fakeroot make -f debian/rules.gen binary-arch_i386_none_686-pae
  • :OPT: If you want to build linux-headers-XXX-common package:
    $ fakeroot make -f debian/rules.gen binary-arch_i386_none_real
  • To clean do:
    $ make -f debian/rules clean

Another way (not tested):

  • cp /boot/config-3.2.0-4-686-pae .config
  • :OPT: make menuconfig
  • make-kpkg --rootcmd fakeroot --initrd -j`grep ^processor /proc/cpuinfo|wc -l` linux-image
  • make-kpkg --rootcmd fakeroot --initrd -j`grep ^processor /proc/cpuinfo|wc -l` linux-headers

Relevant links:

How to submit a kernel patch?

Use:
  • create branch e.g. fix, make changes, commit them
  • git format-patch master..fix
  • scripts/checkpatch.pl --strict 0001-myfix.patch

Send using Thunderbird, but apply the following settings:

  • mailnews.send_plaintext_flowed=false
  • mailnews.wraplength=0
  • mailnews.reply_in_default_charset=true (Display → Advanced → When possible use the default character encoding in replies)

Read:

Can I use variable substitution in debian/control file?

Generally you can (see Variable substitutions: debian/substvars chapter), but this may cause problems for the mandatory fields (see bug#621006).

, , , , , , ,
1) Very nice documentation, I recommend
2) Nice LDAP tree OID browser)
3) See Samba and LDAP section
4) The problem solution is taken from here
5) As manual correctly notices, TLS_CACERTDIR is not used by GNUtls which is used by ldap-utils
6) This file is re-created each time there are changes in ca-certificates package, so more secure is to add a link to /usr/share/ca-certificates and append file name to /etc/ca-certificates.conf
7) “Me TV” didn't work well for me
8) badblocks -w -t random -v -o badblocks-sda /dev/sda
9) means “Intend To Package”
software/linux.txt · Last modified: 2023/01/04 19:57 by dmitry

"Девица не хочет лезть в Окно" – device not compatible with Windows.

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