How to debug Systemd problems

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Foreword

If you are experiencing a problem with system boot up due to Systemd, please see the common bugs document before filing a bug. Some easy configuration tweaks that fix a wide range of issues may be listed there. If the problem you are seeing is not listed there or none of the workarounds seem to help, please consider filing a bug to help us make Fedora run better on your hardware.

Be prepared to include some information (logs) about your system as well. These should be complete (no snippets please), not in an archive, uncompressed, with MIME type set as text/plain.

Contents

Identifying your problem area

  1. Remove rhgb and quiet from the kernel command line.
  2. Add systemd.log_level=debug to the kernel command line to log systemd with debug output enabled.
  3. Add systemd.log_target=kmsg to the kernel command line to let systemd buffer to be written to the kernel log buffer.
  4. Run /bin/systemd --test --system from command line to test run init as systemd.

Information to include in your report

All bug reports

In all cases, the following should be mentioned and attached to your bug report:

  • The exact kernel command-line used if not default. Typically from the bootloader configuration file (e.g. /etc/grub.conf) or from /proc/cmdline
  • A copy of /var/log/messages
  • The output of the dmesg command dmesg > dmesg.txt
  • Systemd dump systemctl dump > systemd_dump.txt


Note.png
If you experience bootup difficulties before systemd starts running, see Debugging Dracut to diagnose that further.
Note.png
If you're system hangs while starting or running udev, see Debugging Udev to diagnose that further.

Configure a serial console

Successfully debugging boot up will require some form of console logging during the system boot. This section documents configuring a serial console connection to record boot messages.

  1. First, enable serial console output for both the kernel and the bootloader.
    • Open the file /etc/grub.conf for editing. Below the line timeout=5, add the following:
      serial --unit=0 --speed=38400
      terminal --timeout=5 serial console
    • Also in /etc/grub.conf, add the following boot arguemnts to the kernel line:
      console=tty0 console=ttyS0,38400
    • When finished, the /etc/grub.conf file should look similar to the example below.
      default=0
      timeout=5
      serial --unit=0 --speed=38400
      terminal --timeout=5 serial console
      title Fedora (2.6.35.4-18.fc14.x86_64)
      root (hd0,0)
      kernel /vmlinuz-2.6.35.4-18.fc14.x86_64 ro root=/dev/mapper/VolGroup-lv_root rd_LVM_LV=VolGroup/lv_root #*:rd_LVM_LV=VolGroup/lv_swap rd_NO_LUKS rd_NO_MD rd_NO_DM LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc #*:KEYTABLE=is-latin1 systemd.log_level=debug systemd.log_target=kmsg console=tty0 console=ttyS0,38400
      initrd /initramfs-2.6.35.4-18.fc14.x86_64.img
    • More detailed information on how to configure the kernel for console output can be found at [1].
Idea.png
Redirecting non-interactive output
You can redirect all non-interactive output to /dev/kmsg and the kernel will put it out on the console when it reaches the kernel buffer by doing
exec >/dev/kmsg 2>&1 </dev/console

Enable shell access early in systemd

You can enable shell access early in systemd startup process to fall back on and diagnose systemd related boot up issues with various systemctl commands should systemd startup otherwise fail.

  • Run echo "openvt -c9 /bin/sh" >> /etc/rc.d/rc.sysinit : To enable shell on tty9.

Various useful systemd related commands

  • Run systemctl list-jobs

To identify slow boot and look for the jobs that are "running" those jobs are the ones where boot waits for completion on and the ones that listed as "waiting" will be executed only after those which are "running" are completed.

  • Run systemctl status ssh.service

To examine the current runtime status of the service. ( In the above example the ssh service )

  • Run systemctl show -p "Wants" multi-user.target

To figure out which services a target pulls in. ( In the above example the multi-user.target )

  • Run {{{1}}}

To examine what gets started when when booted into a specific target. ( In the above example the multi-user.target )

Additional systemd boot parameters

The following boot parameters are also available to further assist with debugging boot issues.

systemd.unit= 
Overrides the unit to activate on boot. This may be used to temporarily boot into a different boot unit, for example rescue.target or emergency.service. ( Defaults to default.target. )
systemd.dump_core= 
Takes a boolean argument. If true systemd dumps core when it crashes. Otherwise no core dump is created. ( Defaults to true )
systemd.crash_shell= 
Takes a boolean argument. If true systemd spawns a shell when it crashes. Otherwise no core dump is created. Defaults to false, for security reasons, as the shell is not protected by any password authentication.
systemd.crash_chvt= 
Takes an integer argument. If positive systemd activates the specified virtual terminal when it crashes. ( Defaults to -1 )
systemd.confirm_spawn= 
Takes a boolean argument. If true asks for confirmation when spawning processes. ( Defaults to false )
systemd.show_status= 
Takes a boolean argument. If true shows terse service status updates on the console during bootup. ( Defaults to true )
systemd.sysv_console= 
Takes a boolean argument. If true output of SysV init scripts will be directed to the console. ( Defaults to true, unless quiet is passed as kernel command line option in which case it defaults to false. )
systemd.log_target= 
Set log target. Argument must be one of console, syslog, kmsg, syslog-or-kmsg, null.
systemd.log_level= 
Set log level. As argument this accepts a numerical log level or the well-known syslog symbolic names (lowercase): emerg, alert, crit, err, warning, notice, info, debug.
systemd.log_color= 
Highlight important log messages. Argument is a boolean value. If the argument is omitted it defaults to true.
systemd.log_location= 
Include code location in log messages. This is mostly relevant for debugging purposes. Argument is a boolean value. If the argument is omitted it defaults to true.