Find the name of the systemd unit for MariaDB or RabbitMQ server.
List all installed services, including disabled services, and search for “maria”:
systemctl list-unit-files --type=service | grep maria
Alternative if you know the package name:
$ rpm -ql mariadb-server|grep service /usr/lib/systemd/system/mariadb.service
List enabled services:
Note: it looks like “list-units” doesn’t show mariadb.service, probably because it is disabled (not started at boot).
System logs: journald and journalctl¶
- Binary logs are written into
- Show syslog from the most recent to the oldest logs:
- Show all logs since the last boot:
journalctl -b 0
- List boots:
tail -f /var/log/syslog:
tail -f /var/log/syslogbut only for apache:
journalctl -u apache.service -f
- Kernel logs of the current boot:
journalctl -k(similar to
dmesgbut with better timestamp)
- Retain only journald logs of the past 30 days:
journalctl _PID=7797show logs of process pid 7797
journalctl _COMM=chronyd -rshows latest logs of the program
- Other fields:
_EXE: program full path
_CMDLINE: program command line with arguments
_UID: user identifier
_GID: group identifier
_BOOT_ID: boot UUID
_MACHINE_ID: machine UUID
- See all journalctl fields:
journalctl -o export
Example of a single log entry (in
__CURSOR=s=c9faccefcf184d67b8a1a1a8c9441d83;i=9417;b=b6852be278a647e3b1f1047604d828c8;m=3e8ae848;t=5a093d6b361fa;x=2c3f533b3fc622ed __REALTIME_TIMESTAMP=1583931706270202 __MONOTONIC_TIMESTAMP=1049290824 _BOOT_ID=b6852be278a647e3b1f1047604d828c8 PRIORITY=6 SYSLOG_FACILITY=3 _UID=1000 _GID=1000 _SELINUX_CONTEXT=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 _AUDIT_SESSION=3 _AUDIT_LOGINUID=1000 _SYSTEMD_OWNER_UID=1000 _SYSTEMD_UNITemail@example.com _SYSTEMD_SLICE=user-1000.slice _SYSTEMD_USER_SLICE=-.slice _MACHINE_ID=1a6df4a3ce76477790264e5d3a9fa609 _HOSTNAME=apu _TRANSPORT=stdout SYSLOG_IDENTIFIER=gnome-shell _COMM=gnome-shell _EXE=/usr/bin/gnome-shell _CMDLINE=/usr/bin/gnome-shell _CAP_EFFECTIVE=800000 _SYSTEMD_CGROUPfirstname.lastname@example.org/gnome-shell-wayland.service _SYSTEMD_USER_UNIT=gnome-shell-wayland.service _PID=1702 _SYSTEMD_INVOCATION_ID=5afe30294e9c49d6b27ff3011323619a _STREAM_ID=e46f4fd89cd3445fbac494d0814d34a5 MESSAGE <80>^@^@^@^@^@^@^@libinput error: client bug: timer event13 debounce short: scheduled expiry is in the past (-5ms), your system is too slow
Advantages over scattered text log files:
- Timestamps seem to be more reliable, especially for kernel logs
- Ability to display logs in the reverse order
- Ability to filter logs by service, by user, by process pid, by boot, etc.
- … in fact, I rarely use logs, so I don’t have strong expectations for logs :-)
Advantages of systemd to run services¶
- I like systemd global design to build “stateless” services, by isolating them from the system for example.
- Security: systemd gives access to high level security protections like
running a service with its own private temporary directory
- Read also Using systemd for more secure services in Fedora
- systemd can even create a couple of temporary (user, group) to run a service
and remove theme once the service stops. To be able to implement this
feature, systemd has to cleanup all resources owner by the user. Running
the service with a read-only filesystem except of a single writable directory
helps to remove all files created by the service. Removing all IPC owned by
a user is part of this cleanup (option
systemctl status serviceshows the last log lines.
- Thanks to cgroups, systemd is able to list all processes of a service in a
systemctl status servicelists all process identfiers of the service (main pid, but also pids of child processes). Moreover, when systemd stops a service, the usage of a cgroups makes sure that all processes are killed. Bye bye the legacy and annoying “pid file” causing so many troubles.
- The simple
.servicefile format makes it much easier to share these files between Linux distributions. Linux distributions can collaborate on more complex issues like handling properly NFS mounts: Systemd programming, 30 months later. Moreover, it’s easier to enable security protections for all Linux distributions.
There is a similar trend to isolate desktop applications using sandboxes: see Flatpak. For security, but also to reduce dependencies to the system, and so run an old application on a newer system, or the opposite. Embedding libraries in Flatpak “containers” comes with its own set of issues, but that’s a different topic ;-)
See also Fedora ABRT.
coredumpctl checks for coredump in
$ coredumpctl list TIME PID UID GID SIG COREFILE EXE Wed 2020-03-11 13:46:38 CET 3350 1000 1000 11 present /usr/bin/python3.7 Wed 2020-03-11 13:48:28 CET 2211 1000 1000 11 present /usr/bin/abrt-applet $ coredumpctl dump /usr/bin/abrt-applet > core PID: 2211 (abrt-applet) (...) Signal: 11 (SEGV) Timestamp: Wed 2020-03-11 13:48:27 CET (30min ago) Command Line: /usr/bin/abrt-applet --gapplication-service (...) Storage: /var/lib/systemd/coredump/core.abrt-applet.1000.b6852be278a647e3b1f1047604d828c8.2211.1583930907000000000000.lz4 Message: Process 2211 (abrt-applet) of user 1000 dumped core. Stack trace of thread 2211: #0 0x00007f978e419fec problem_get_argv0 (libreport-gtk.so.0) #1 0x00005632d09a4d83 notify_problem_list (abrt-applet) #2 0x00005632d09a5291 show_problem_list_notification (abrt-applet) (...)
systemd features are not unique, it’s totally doable without sytemd.
Right, but systemd comes with a simple configuration files (.service files) which gives an easy access to these features.
systemd has bugs!
Right, as any other software. And they are quickly fixed.
systemd developers reject patches to support platforms other than Linux:
Ok, this is a real issue. I have no answer for that one :-)
BSD systems don’t use systemd but reimplemented the strict minimum systemd APIs required by Gnome.