Note: This is a RHCSA 7 exam objective.
Most of system log files are located in the /var/log directory due to SYSLOG default configuration (see /etc/rsyslog.conf file).
In addition, all SELinux events are written into the /var/log/audit/audit.log file.
With Systemd, new commands have been created to analyse logs at boot time and later.
Systemd primary task is to manage the boot process and provides informations about it.
To get the boot process duration, type:
# systemd-analyze Startup finished in 422ms (kernel) + 2.722s (initrd) + 9.674s (userspace) = 12.820s
To get the time spent by each task during the boot process, type:
# systemd-analyze blame 7.029s network.service 2.241s plymouth-start.service 1.293s kdump.service 1.156s plymouth-quit-wait.service 1.048s firewalld.service 632ms postfix.service 621ms tuned.service 460ms iprupdate.service 446ms iprinit.service 344ms accounts-daemon.service ... 7ms systemd-update-utmp-runlevel.service 5ms systemd-random-seed.service 5ms sys-kernel-config.mount
Note: You will find additional information on this point in the Lennart Poettering’s blog.
In addition, Systemd handles the system event log, a syslog daemon is not mandatory any more.
The reasons behind Journald creation are explained in this Introduction to Journald.
To get the content of the Systemd journal, type:
To get all the events related to the crond process in the journal, type:
# journalctl /sbin/crond
Note: You can replace /sbin/crond by `which crond`.
Altenatively, to get all the events related to the crond process, you can also type:
# journalctl -u crond
To get all the events since the last boot, type:
# journalctl -b
To get all the events that appeared today in the journal, type:
# journalctl --since=today
To get all the events with a syslog priority of err, type:
# journalctl -p err
To get the 10 last events and wait for any new one (like tail -f /var/log/messages), type:
# journalctl -f
By default, Journald logs are stored in the /run/log/journal directory and disappear after a reboot.
To store Journald logs in a more permanent way, type:
# mkdir /var/log/journal # echo "SystemMaxUse=50M" >> /etc/systemd/journald.conf # systemctl restart systemd-journald
Note: Setting the SystemMaxUse variable is necessary because otherwise 10% of the filesystem where the /var/log/journal directory is stored may be used at maximum by the journal.
There is a tutorial dedicated to Systemd that presents additional information about the Systemd journal.
The rsyslog.com website provides some interesting information about rsyslogd (features, modules, plugins, etc).
Fedora Magazine also published an interesting article, Systemd: Using the journal.
Rainer Gerhards, rsyslog main author, discusses the arguments around the creation of Journald.
Nikolai Bezroukov wrote an authoritative page about Syslog.
The FreeIPA project (Identity Management with Kerberos, LDAP and Apache) provides several useful resources about Centralized Logging or Logging with Logstash/ElasticSearch/Kibana.
Logs can get flooded by some Systemd messages (starting sessions, etc). Red Hat provides a way to get rid of useless Systemd messages.