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I have created a simple systemd service file for a custom application. The application works well when I run it manually, but my CPU gets maxed out when I run it with systemd.

I'm trying do track down where my problem is, but I don't know where to find the output (or how to configure systemd to put the output somewhere).

Here is my service file:

Description=Syncs files with a server when they change

ExecStart=/usr/local/bin/filesync-client --port 2500


Throughout the application, I output to stdout and stderr.

How can I read the output of my daemon?


I found man systemd.exec, which mentioned the StandardOutput= option, but I'm not sure how to use it. From the man page:


Controls where file descriptor 1 (STDOUT) of the executed processes is connected to. Takes one of inherit, null, tty, syslog, kmsg, kmsg+console, syslog+console or socket.

If set to inherit the file descriptor of standard input is duplicated for standard output. If set to null standard output will be connected to /dev/null, i.e. everything written to it will be lost. If set to tty standard output will be connected to a tty (as configured via TTYPath=, see below). If the TTY is used for output only the executed process will not become the controlling process of the terminal, and will not fail or wait for other processes to release the terminal. syslog connects standard output to the syslog(3) system logger. kmsg connects it with the kernel log buffer which is accessible via dmesg(1). syslog+console and kmsg+console work similarly but copy the output to the system console as well. socket connects standard output to a socket from socket activation, semantics are similar to the respective option of StandardInput=. This setting defaults to inherit.

Does this mean that these are my only options? I would like, for example, to put output in /dev/shm or something. I suppose I could use a unix domain socket and write a simple listener, but this seems a little unnecessary.

I just need this for debugging, and I'll probably end up removing most of the logs and change the output to syslog.

share|improve this question
Have you tried checking /var/log/syslog for output? Most systems will log stuff into /var/log/ so I'd start by checking there. You can use grep to search for text if you know the output: grep "my output" /var/log should do the trick. – sbtkd85 Sep 9 '11 at 19:10
@sbtkd85 - Well, I don't have /var/log/syslog, but /var/log/messages does the trick. The problem is, according to the logs, my daemon crashes on start, yet I can tell that it is still running because it has an HTTP server, and I can query it. It seems the rest of the logs are getting lost... – tjameson Sep 10 '11 at 3:50
Why not try setting StandardOutput=tty so you can see what is happening when you launch your daemon. It should output the terminal (you may have to use ttyS0 or similar to get the output on your screen). – sbtkd85 Sep 12 '11 at 13:46
Shouldn't standard IO redirection operators work in this context. Something like ExecStart=/usr/local/bin/filesync-client --port 2500 2>/tmp/filesync.log – Deepak Mittal Apr 10 '12 at 18:30
What is actually abusing your CPU? Is it systemd, your service or system (e.g. by spawning new copies of the service because systemd went crazy)? – peterph Nov 13 '12 at 16:03
up vote 32 down vote accepted

By default stdout and stderr of a systemd unit are sent to syslog.

If you're using the full systemd, this will be accesible via journalctl. On Fedora, it should be /var/log/messages but syslog will put it where your rules say.

Due to the date of the post, and assuming most people that are exposed to systemd are via fedora, you were probably hit by the bug described here: https://bugzilla.redhat.com/show_bug.cgi?id=754938 It has a good explanation of how it all works too =) (This was a bug in selinux-policy that caused error messages to not be logged, and was fixed in selinux-policy-3.10.0-58.fc16)


As mikemaccana notes, the systemd journal is now the standard logging device in most places. To get stdout and stderr of a unit in a pager.

journalctl -u [unit]

Leaving the above as that wasn't the case for this question.

share|improve this answer
Note that using the standard logging mechanism like this will not create persistent logs by default. To do that, you'll need to create /var/log/journal, and then run sudo systemctl restart systemd-journald – mlissner May 8 '15 at 2:21
what syslog facility and priority? – jrwren Jul 7 '15 at 16:31
This worked for me: StandardOutput=syslog+console and StandardError=syslog+console after that all output from my unit appeared in journalctl. The default setting was wrong apparently. (Such as DefaultStandardOutput in /etc/systemd/system.conf) – gregn3 Jul 22 '15 at 12:23

Shorter, simpler, non-legacy answer:

sudo journalctl -u [unitfile]

Where [unitfile] is the systemd .service name. Eg, to see messages from docker.service,

sudo journalctl --unit=docker
share|improve this answer
Note that you might have to sudo if you get a No journal files found error. – bigjosh Nov 17 '15 at 15:51

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