35 - systemd Timers

35.1 Concept

Systemd is manager of everything in Linux.
- systemctl is the main management tool (give order, ask questions) for systemd.
Unit is a configuration text file that defines how process work.
Timer is a unit file ending in .timer that acts as an alarm clock.
- Exp: Task scheduling & alarm execution
- .timer will trigger corresponding .service file when a time threshold or event is reached.

35.2 Example of Timer 1: logrotate

logrotate is package (similar software in Windows OS) in Linux.
Log files generated by the system and running applications continue to grow over time.
- logrotate prevents this issue by periodically renames existing active log files, automatically compresses rotated historical log files etc.
systemd executes the logrotate command.
- The logrotate.timer triggers logrotate.service once per day to clean up and rotates the logs.
Refer to 42 - logrotate for tutorial.

35.3 Example of Timer 2: sysstat

sysstat is package (similar software in Windows OS) in Linux.
It collects, records, and analyzes real-time and historical system performance metrics.
The sysstat-collect.timer triggers sysstat-collect.service every 10 minutes to capture snapshot system performance metrics.

Tutorial

Install sysstat
- dnf install -y sysstat
Checks sysstat units files
- systemctl list-unit-files sysstat*
Enable timer
- sudo systemctl enable --now [Timer Unit].timer
- Example: sudo systemctl enable --now sysstat-collect.timer
Displays the status of the timer
- systemctl status [Timer Unit].timer
- Example: systemctl status sysstat-collect.timer
Trigger the service now
- sudo systemctl start [Timer Unit].service
- Example: sudo systemctl start sysstat-collect.service
sar (System Activity Reporter) displays CPU usage, memory utilization, network statistics, and I/O metrics.
- sar -A
Displays the status of the sysstat-collect.service
- systemctl status sysstat-collect.service
Check the configuration of the sysstat-collect.service
- systemctl cat sysstat-collect.service
Displays the status of the sysstat-collect.timer
- systemctl status sysstat-collect.timer
Check the configuration of the sysstat-collect.timer
- systemctl cat sysstat-collect.timer

Result

student@localhost:~$ sudo dnf install -y sysstat

[sudo] password for student:

Updating Subscription Management repositories.

Last metadata expiration check: 0:43:08 ago on Tue 01 Sep 2026 04:06:39 PM +08.

Dependencies resolved.

=============================================================================================================================================================

Package Architecture Version Repository Size

=============================================================================================================================================================

Installing:

sysstat x86_64 12.7.6-4.el10 rhel-10-for-x86_64-appstream-rpms 532 k

Installing dependencies:

lm_sensors-libs x86_64 3.6.0-20.el10 rhel-10-for-x86_64-appstream-rpms 43 k

pcp-conf x86_64 7.0.3-5.el10_2 rhel-10-for-x86_64-appstream-rpms 37 k

pcp-libs x86_64 7.0.3-5.el10_2 rhel-10-for-x86_64-appstream-rpms 802 k

Transaction Summary

=============================================================================================================================================================

Install 4 Packages

Total download size: 1.4 M

Installed size: 4.2 M

Downloading Packages:

(1/4): lm_sensors-libs-3.6.0-20.el10.x86_64.rpm 55 kB/s | 43 kB 00:00

(2/4): pcp-conf-7.0.3-5.el10_2.x86_64.rpm 36 kB/s | 37 kB 00:01

(3/4): sysstat-12.7.6-4.el10.x86_64.rpm 352 kB/s | 532 kB 00:01

(4/4): pcp-libs-7.0.3-5.el10_2.x86_64.rpm 377 kB/s | 802 kB 00:02

-------------------------------------------------------------------------------------------------------------------------------------------------------------

Total 485 kB/s | 1.4 MB 00:02

Running transaction check

Transaction check succeeded.

Running transaction test

Transaction test succeeded.

Running transaction

Preparing : 1/1

Installing : pcp-conf-7.0.3-5.el10_2.x86_64 1/4

Installing : pcp-libs-7.0.3-5.el10_2.x86_64 2/4

Installing : lm_sensors-libs-3.6.0-20.el10.x86_64 3/4

Installing : sysstat-12.7.6-4.el10.x86_64 4/4

Running scriptlet: sysstat-12.7.6-4.el10.x86_64 4/4

Created symlink '/etc/systemd/system/multi-user.target.wants/sysstat.service' → '/usr/lib/systemd/system/sysstat.service'.

Created symlink '/etc/systemd/system/sysstat.service.wants/sysstat-collect.timer' → '/usr/lib/systemd/system/sysstat-collect.timer'.

Created symlink '/etc/systemd/system/sysstat.service.wants/sysstat-summary.timer' → '/usr/lib/systemd/system/sysstat-summary.timer'.

Created symlink '/etc/systemd/system/sysstat.service.wants/sysstat-rotate.timer' → '/usr/lib/systemd/system/sysstat-rotate.timer'.

Installed products updated.

Installed:

lm_sensors-libs-3.6.0-20.el10.x86_64 pcp-conf-7.0.3-5.el10_2.x86_64 pcp-libs-7.0.3-5.el10_2.x86_64 sysstat-12.7.6-4.el10.x86_64

Complete!

student@localhost:~$ systemctl list-unit-files sysstat*

UNIT FILE STATE PRESET

sysstat-collect.service static -

sysstat-rotate.service static -

sysstat-summary.service static -

sysstat.service enabled enabled

sysstat-collect.timer enabled enabled

sysstat-rotate.timer enabled disabled

sysstat-summary.timer enabled enabled

7 unit files listed.

student@localhost:~$ systemctl start sysstat-collect.service

student@localhost:~$ sar -A

Linux 6.12.0-211.43.1.el10_2.x86_64 (localhost.localdomain) 09/01/2026 _x86_64_ (2 CPU)

05:00:50 PM CPU %usr %nice %sys %iowait %steal %irq %soft %guest %gnice %idle

05:02:23 PM all 0.79 0.00 1.40 0.02 0.00 2.25 0.50 0.00 0.00 95.04

05:02:23 PM 0 1.10 0.00 1.30 0.01 0.00 2.44 0.60 0.00 0.00 94.55

05:02:23 PM 1 0.48 0.00 1.50 0.02 0.00 2.06 0.40 0.00 0.00 95.54

Average: CPU %usr %nice %sys %iowait %steal %irq %soft %guest %gnice %idle

Average: all 0.79 0.00 1.40 0.02 0.00 2.25 0.50 0.00 0.00 95.04

Average: 0 1.10 0.00 1.30 0.01 0.00 2.44 0.60 0.00 0.00 94.55

Average: 1 0.48 0.00 1.50 0.02 0.00 2.06 0.40 0.00 0.00 95.54

05:00:50 PM proc/s cswch/s

05:02:23 PM 0.86 500.82

Average: 0.86 500.82

05:00:50 PM pswpin/s pswpout/s

05:02:23 PM 0.00 0.00

Average: 0.00 0.00

05:00:50 PM pgpgin/s pgpgout/s fault/s majflt/s pgfree/s pgscank/s pgscand/s pgsteal/s pgprom/s pgdem/s

05:02:23 PM 0.47 12.00 775.52 0.01 345.98 0.00 0.00 0.00 0.00 0.00

Average: 0.47 12.00 775.52 0.01 345.98 0.00 0.00 0.00 0.00 0.00

05:00:50 PM tps rtps wtps dtps bread/s bwrtn/s bdscd/s

05:02:23 PM 0.63 0.03 0.60 0.00 0.94 23.99 0.00

Average: 0.63 0.03 0.60 0.00 0.94 23.99 0.00

05:00:50 PM kbmemfree kbavail kbmemused %memused kbbuffers kbcached kbcommit %commit kbactive kbinact kbdirty kbanonpg kbslab kbkstack kbpgtbl kbvmused

05:02:23 PM 464156 1565060 1819680 48.64 5268 1303648 6329352 99.48 2054184 836096 408 1569620 148152 12844 27500 36020

Average: 464156 1565060 1819680 48.64 5268 1303648 6329352 99.48 2054184 836096 408 1569620 148152 12844 27500 36020

05:00:50 PM kbswpfree kbswpused %swpused kbswpcad %swpcad

05:02:23 PM 2617828 3608 0.14 44 1.22

Average: 2617828 3608 0.14 44 1.22

05:00:50 PM kbhugfree kbhugused %hugused kbhugrsvd kbhugsurp

05:02:23 PM 0 0 0.00 0 0

Average: 0 0 0.00 0 0

05:00:50 PM dentunusd file-nr inode-nr pty-nr

05:02:23 PM 46806 9568 50737 1

Average: 46806 9568 50737 1

05:00:50 PM runq-sz plist-sz ldavg-1 ldavg-5 ldavg-15 blocked

05:02:23 PM 5 801 0.27 0.71 0.55 0

Average: 5 801 0.27 0.71 0.55 0

05:00:50 PM DEV tps rkB/s wkB/s dkB/s areq-sz aqu-sz await %util

05:02:23 PM sda 0.63 0.47 12.00 0.00 19.69 0.00 4.49 0.06

05:02:23 PM dm-0 0.76 0.47 12.00 0.00 16.36 0.00 5.41 0.06

05:02:23 PM dm-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Average: sda 0.63 0.47 12.00 0.00 19.69 0.00 4.49 0.06

Average: dm-0 0.76 0.47 12.00 0.00 16.36 0.00 5.41 0.06

Average: dm-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

05:00:50 PM IFACE rxpck/s txpck/s rxkB/s txkB/s rxcmp/s txcmp/s rxmcst/s %ifutil

05:02:23 PM lo 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

05:02:23 PM enp0s3 25.73 0.64 2.21 0.05 0.00 0.00 11.76 0.00

Average: lo 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Average: enp0s3 25.73 0.64 2.21 0.05 0.00 0.00 11.76 0.00

05:00:50 PM IFACE rxerr/s txerr/s coll/s rxdrop/s txdrop/s txcarr/s rxfram/s rxfifo/s txfifo/s

05:02:23 PM lo 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

05:02:23 PM enp0s3 0.00 0.00 0.00 0.03 0.00 0.00 0.00 0.00 0.00

Average: lo 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Average: enp0s3 0.00 0.00 0.00 0.03 0.00 0.00 0.00 0.00 0.00

05:00:50 PM call/s retrans/s read/s write/s access/s getatt/s

05:02:23 PM 0.00 0.00 0.00 0.00 0.00 0.00

Average: 0.00 0.00 0.00 0.00 0.00 0.00

05:00:50 PM scall/s badcall/s packet/s udp/s tcp/s hit/s miss/s sread/s swrite/s saccess/s sgetatt/s

05:02:23 PM 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Average: 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

05:00:50 PM totsck tcpsck udpsck rawsck ip-frag tcp-tw

05:02:23 PM 882 19 2 0 0 1

Average: 882 19 2 0 0 1

05:00:50 PM CPU total/s dropd/s squeezd/s rx_rps/s flw_lim/s blg_len

05:02:23 PM all 25.73 0.00 0.10 0.00 0.00 0

05:02:23 PM 0 25.73 0.00 0.10 0.00 0.00 0

05:02:23 PM 1 0.00 0.00 0.00 0.00 0.00 0

Average: CPU total/s dropd/s squeezd/s rx_rps/s flw_lim/s blg_len

Average: all 25.73 0.00 0.10 0.00 0.00 0

Average: 0 25.73 0.00 0.10 0.00 0.00 0

Average: 1 0.00 0.00 0.00 0.00 0.00 0

student@localhost:~$ systemctl status sysstat-collect.service

○ sysstat-collect.service - system activity accounting tool

Loaded: loaded (/usr/lib/systemd/system/sysstat-collect.service; static)

Active: inactive (dead) since Tue 2026-09-01 17:02:23 +08; 3min 46s ago

Invocation: 5fe21adedb064804b9b026aff0cf5e86

TriggeredBy: ● sysstat-collect.timer

Docs: man:sa1(8)

Process: 6303 ExecStart=/usr/lib64/sa/sa1 1 1 (code=exited, status=0/SUCCESS)

Main PID: 6303 (code=exited, status=0/SUCCESS)

Mem peak: 1.2M

CPU: 16ms

Sep 01 17:02:23 localhost.localdomain systemd[1]: Starting sysstat-collect.service - system activity accounting tool...

Sep 01 17:02:23 localhost.localdomain systemd[1]: sysstat-collect.service: Deactivated successfully.

Sep 01 17:02:23 localhost.localdomain systemd[1]: Finished sysstat-collect.service - system activity accounting tool.

student@localhost:~$ systemctl cat sysstat-collect.service

# /usr/lib/systemd/system/sysstat-collect.service

#

# sysstat-12.7.6 systemd unit file:

# Collects system activity data

# Activated by sysstat-collect.timer unit

[Unit]

Description=system activity accounting tool

Documentation=man:sa1(8)

After=sysstat.service

[Service]

Type=oneshot

User=root

ExecStart=/usr/lib64/sa/sa1 1 1

student@localhost:~$ systemctl status sysstat-collect.timer

● sysstat-collect.timer - Run system activity accounting tool every 10 minutes

Loaded: loaded (/usr/lib/systemd/system/sysstat-collect.timer; enabled; preset: enabled)

Active: active (waiting) since Tue 2026-09-01 16:55:00 +08; 11min ago

Invocation: 774f8e9bfe2d4bbdbba911c44879bd32

Trigger: Tue 2026-09-01 17:10:00 +08; 3min 29s left

Triggers: ● sysstat-collect.service

Sep 01 16:55:00 localhost.localdomain systemd[1]: Started sysstat-collect.timer - Run system activity accounting tool every 10 minutes.

student@localhost:~$ systemctl cat sysstat-collect.timer

# /usr/lib/systemd/system/sysstat-collect.timer

#

# sysstat-12.7.6 systemd unit file:

# Activates activity collector every 10 minutes

[Unit]

Description=Run system activity accounting tool every 10 minutes

[Timer]

OnCalendar=*:00/10

[Install]

WantedBy=sysstat.service

student@localhost:~$

References

rhcsa-9-ex200/lessons/Lesson-16-Task-Scheduling.md at main · dverbeeck/rhcsa-9-ex200