Back to systemd

Diagnosing Boot Problems

If your machine gets stuck during boot, first check if the hang happens before or after control passes to systemd.

Try to boot without rhgb and quiet on the kernel command line. If you see some messages like these:

  • Welcome to Fedora VERSION (codename)!"
  • Starting name...
  • [ OK ] Started name.

then systemd is running. (See an actual screenshot.)

Debugging always gets easier if you can get a shell. If you do not get a login prompt, try switching to a different virtual terminal using CTRL+ALT+F__. Problems with X server startup may manifest themselves as a missing login on tty1, but other VTs working.

If the boot stops without presenting you with a login on any virtual console, let it retry for up to 5 minutes before declaring it definitely stuck. There is a chance that a service that has trouble starting will be killed after this timeout and the boot will continue normally. Another possibility is that a device for an important mountpoint will fail to appear and you will be presented with emergency mode.

If You Get No Shell

If you get neither a normal login nor the emergency mode shell, you will need to do additional steps to get debugging information out of the machine.

  • Try CTRL+ALT+DEL to reboot.
    • If it does not reboot, mention it in your bugreport. Meanwhile force the reboot with SysRq or hard reset.
  • When booting the next time, you will have to add some kernel command line arguments depending on which of the debugging strategies you choose from the following options.

Debug Logging to a Serial Console

If you have a hardware serial console available or if you are debugging in a virtual machine (e.g. using virt-manager you can switch your view to a serial console in the menu View -> Text Consoles), you can ask systemd to log lots of useful debugging information to it by booting with:

systemd.log_level=debug systemd.log_target=console console=ttyS0,38400

Booting into Rescue or Emergency Targets

To boot directly into rescue target add systemd.unit=rescue.target or just 1 to the kernel command line. This target is useful if the problem occurs somewhere after the basic system is brought up, during the starting of "normal" services. If this is the case, you should be able to disable the bad service from here. If the rescue target will not boot either, the more minimal emergency target might.

To boot directly into emergency shell add systemd.unit=emergency.target or emergency to the kernel command line. Note that in the emergency shell you will have to remount the root filesystem read-write by yourself before editing any files:

mount -o remount,rw /

Common issues that can be resolved in the emergency shell are bad lines in /etc/fstab. After fixing /etc/fstab, run systemctl daemon-reload to let systemd refresh its view of it.

If not even the emergency target works, you can boot directly into a shell with init=/bin/sh. This may be necessary in case systemd itself or some libraries it depends on are damaged by filesystem corruption. You may need to reinstall working versions of the affected packages.

If init=/bin/sh does not work, you must boot from another medium.

Early Debug Shell

You can enable shell access to be available very early in the startup process to fall back on and diagnose systemd related boot up issues with various systemctl commands. Enable it using:

systemctl enable debug-shell.service

Tip: If your version of systemd is not new enough to have debug-shell.service, you can download the unit file from systemd git. Substitute /bin/bash for @sushell@ in the file.

Tip: If you find yourself in a situation where you cannot use systemctl (e.g. when setting this up from a different booted system), you can enable the service manually:

cd $PATH_TO_YOUR_ROOT_FS/etc/systemd/system
mkdir -p sysinit.target.wants
ln -s /usr/lib/systemd/system/debug-shell.service sysinit.target.wants/

Once enabled, the next time you boot you will be able to switch to tty9 using CTRL+ALT+F9 and have a root shell there available from an early point in the booting process. You can use the shell for checking the status of services, reading logs, looking for stuck jobs with systemctl list-jobs, etc.

Warning: Use this shell only for debugging! Do not forget to disable systemd-debug-shell.service after you've finished debugging your boot problems. Leaving the root shell always available would be a security risk.

verify prerequisites

A (at least partly) populated /dev is required. Depending on your setup (e.g. on embedded systems), check that the Linux kernel config options CONFIG_DEVTMPFS and CONFIG_DEVTMPFS_MOUNT are set. Also support for cgroups and fanotify is recommended for a flawless operation, so check that the Linux kernel config options CONFIG_CGROUPS and CONFIG_FANOTIFY are set. The message "Failed to get D-Bus connection: No connection to service manager." during various systemctl operations is an indicator that these are missing.

If You Can Get a Shell

When you have systemd running to the extent that it can provide you with a shell, please use it to extract useful information for debugging. Boot with these parameters on the kernel command line:

systemd.log_level=debug systemd.log_target=kmsg log_buf_len=1M

in order to increase the verbosity of systemd, to let systemd write its logs to the kernel log buffer, and to increase the size of the kernel log buffer. After reaching the shell, save the log:

dmesg > dmesg.txt

When reporting a bug, attach the dmesg.txt file.

To check for possibly stuck jobs use:

systemctl list-jobs

The jobs that are listed as "running" are the ones that must complete before the "waiting" ones will be allowed to start executing.

Diagnosing Shutdown Problems

Just like with boot problems, when you encounter a hang during shutting down, make sure you wait at least 5 minutes to distinguish a permanent hang from a broken service that's just timing out. Then it's worth testing whether the system reacts to CTRL+ALT+DEL in any way.

If shutdown (whether it be to reboot or power-off) of your system gets stuck, first test if the kernel itself is able to reboot or power-off the machine forcedly using one of these commands:

sync && reboot -f
sync && poweroff -f

If either one of the commands does not work, it is a kernel bug, not systemd.

Shutdown Completes Eventually

If normal reboot or poweroff work, but take a suspiciously long time, then

  • boot with the debug options:

    systemd.log_level=debug systemd.log_target=kmsg log_buf_len=1M enforcing=0
    
  • save the following script as /usr/lib/systemd/system-shutdown/debug.sh and make it executable:

    #!/bin/sh
    mount -o remount,rw /
    dmesg > /shutdown-log.txt
    mount -o remount,ro /
    
  • reboot

Look for timeouts logged in the resulting file shutdown-log.txt and/or attach it to a bugreport.

Shutdown Never Finishes

If normal reboot or poweroff never finish even after waiting a few minutes, the above method to create the shutdown log will not help and the log must be obtained using other methods. Two options that are useful for debugging boot problems can be used also for shutdown problems:

  • use a serial console
  • use a debug shell - not only is it available from early boot, it also stays active until late shutdown.

Status and Logs of Services

When the start of a service fails, systemctl will give you a generic error message:

# systemctl start foo.service
Job failed. See system journal and 'systemctl status' for details.

The service may have printed its own error message, but you do not see it, because services run by systemd are not related to your login session and their outputs are not connected to your terminal. That does not mean the output is lost though. By default the stdout, stderr of services are directed to the systemd journal and the logs that services produce via syslog(3) go there too. systemd also stores the exit code of failed services. Let's check:

# systemctl status foo.service
foo.service - mmm service
          Loaded: loaded (/etc/systemd/system/foo.service; static)
          Active: failed (Result: exit-code) since Fri, 11 May 2012 20:26:23 +0200; 4s ago
         Process: 1329 ExecStart=/usr/local/bin/foo (code=exited, status=1/FAILURE)
          CGroup: name=systemd:/system/foo.service

May 11 20:26:23 scratch foo[1329]: Failed to parse config

In this example the service ran as a process with PID 1329 and exited with error code 1. If you run systemctl status as root or as a user from the adm group, you will get a few lines from the journal that the service wrote. In the example the service produced just one error message.

To list the journal, use the journalctl command.

If you have a syslog service (such as rsyslog) running, the journal will also forward the messages to it, so you'll find them in /var/log/messages (depending on rsyslog's configuration).

Reporting systemd Bugs

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.

Please report bugs to your distribution's bug tracker first. If you are sure that you are encountering an upstream bug, then first check for existing bug reports, and if your issue is not listed file a new bug.

Information to Attach to a Bug Report

Whenever possible, 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. /boot/grub2/grub.cfg) or from /proc/cmdline
  • A copy of the file /var/log/messages
  • The output of the dmesg command: dmesg > dmesg.txt
    • ideally after booting with systemd.log_level=debug systemd.log_target=kmsg log_buf_len=1M
  • The output of a systemd dump: systemctl dump > systemd-dump.txt
  • The output of /usr/bin/systemd --test --system --log-level=debug > systemd-test.txt 2>&1