It slows my system boot time.
Can i disable it?
What will happen if i disable it on boot?
I am using Ubuntu version 18.04.
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systemd-journal-flush.service asks the journal daemon to flush any log data stored in /run/log/journal into /var/log/journal, if
persistent storage is enabled. In case you have (already) huge log files, this will result in slower booting. Further the disk (with
/var/log) has to be mounted in a writeable modus to do so.
To sum it up: huge old log files, which are checked during boot and the appending of new log data results in slower boot time.
To check the journalctl log size type
In order to get the time and disk space information of flush processing, enter the following command
journalctl -b --unit systemd-journald
The corresponding output will look like
-- Logs begin at Sat 2018-12-08 00:40:23 CET, end at Mon 2018-12-10 19:40:27 CET. -- Dec 10 12:51:38 ubuntu01 systemd-journald: Journal started Dec 10 12:51:38 ubuntu01 systemd-journald: Runtime journal (/run/log/journal/265c93c062bf4c8da41abfe2ae793452) is 4.7M, max 38.3M, 33.5M free. Dec 10 12:51:38 ubuntu01 systemd-journald: Time spent on flushing to /var is 7.066904s for 132 entries. Dec 10 12:51:38 ubuntu01 systemd-journald: System journal (/var/log/journal/265c93c062bf4c8da41abfe2ae793452) is 128.0M, max 256.0M, 128M free.
Then it is possible that not all log data is written to disk; annoying when debugging boot faults. Journald is a fundamental service in systemd linux and many other services depends on it.
Verify the journal file for internal consistency:
Look out that every journal shows up PASS.
--vacuum-size=BYTES Reduce disk usage below specified size
--vacuum-files=INT Leave only the specified number of journal files
--vacuum-time=TIME Remove journal files older than specified time
Hence do a
sudo journalctl --vacuum-size=1G --vacuum-time=5d --vacuum-files=5
First check your storage type with
systemctl cat systemd-journal-flush.service | grep -i storage
Controls where to store journal data. One of "volatile", "persistent", "auto" and "none".
If "volatile", journal log data will be stored only in memory, i.e. below the /run/log/journal hierarchy (which is created if needed).
If "persistent", data will be stored preferably on disk, i.e. below the /var/log/journal hierarchy (which is created if needed), with a fallback to /run/log/journal (which is created if needed), during early boot and if the disk is not writable.
"auto" is similar to "persistent" but the directory /var/log/journal is not created if needed, so that its existence controls where log data goes.
"none" turns off all storage, all log data received will be dropped. Forwarding to other targets, such as the console, the kernel log buffer, or a syslog socket will still work however. Defaults to "auto".
Edit the file
sudo nano /etc/systemd/journald.conf
In the journal section uncomment and alter:
Storage=auto SystemMaxUse=200M SystemKeepFree=1G SystemMaxFileSize=1G SystemMaxFiles=5
I recommend to limit the size of the SystemMaxFileSize key to 50MB -->
Finally, in case your Ubuntu is not running on an important server, I suggest to change the data storage to volatile:
SystemMaxUse control how much disk space the journal may use up at most.
RuntimeKeepFree control how much disk space systemd-journald shall leave free for other uses. systemd-journald will respect both limits and use the smaller of the two values.
If you run the boot in debug mode and trace the system calls (strace) you may found out that the flush writing has a very poor i/o performance. In my case it was unclear why. Maybe some kernel messages spam the log file (note that after 10000 messages the unit is blocked per default, but journald has to manage this, which maybe cause the poor performance). In that case step over the messages and search for errors, which haven't necessarily marked as errors.
journalctl -b --output short-monotonic
journalctl -b -p 1..4 --output short-monotonic
--output short-monotonicflag prints the time steps in contrast to the default utc time.
Finally remove the old log files by
sudo rm -rf /var/log/journal
Save & reboot.
According to this post from the systemd developer homepage, you can fix it by changing the Unit file.
To do so, open
sudo vim /lib/systemd/system/systemd-journal-flush.service
and change the Before dependency from
This fix will be automatically altered for systemd versions > v240.
Don't forget to save the file.