Lab 11.1: Manage and change services

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Doel

Install a web server, make it start at boot, make it restart by itself after a crash, block a service, and add a small service of your own.

Voordat je begint

Work on server1 as root. A repository must be available (lab 9.1).

Taken

Install httpd. Start it now and make sure it also starts at boot.
Show if httpd is active and enabled, with two short commands.
Change httpd (without editing the file from the package) so that it is always restarted 5 seconds after it stops for any reason.
Kill the main httpd process with SIGKILL and show that systemd starts it again.
Make sure that the service nftables can never be started by accident, then try to start it.
Create the service hello that writes "hello" and the date to the journal every minute. It must start at boot.

Controleer je werk

#systemctl is-active httpd; systemctl is-enabled httpd
#systemctl cat httpd | tail -4
#systemctl status httpd | grep 'Main PID'
#systemctl is-enabled nftables
#journalctl -u hello --since -5min

httpd: active and enabled; the override shows Restart=always and RestartSec=5.
After the kill, the Main PID is new.
nftables: masked.
hello: lines with "hello" in the journal; systemctl is-enabled hello = enabled.

Hints

Toon de hints

systemctl enable --now.
systemctl edit httpd writes a drop-in file.
systemctl kill -s KILL httpd or kill -9 on the Main PID.
systemctl mask.
A unit file in /etc/systemd/system/ with [Install] WantedBy=multi-user.target.

Oplossing

Toon de oplossing

Install and enable.

#dnf install -y httpd
#systemctl enable --now httpd

Short checks.

#systemctl is-active httpd; systemctl is-enabled httpd

The override: add these lines in the editor.
```
#systemctl edit httpd
```
/etc/systemd/system/httpd.service.d/override.conf
```
[Service]
Restart=always
RestartSec=5
```

Kill and watch it come back.

#systemctl kill -s KILL --kill-whom=main httpd
#sleep 6; systemctl status httpd | grep -E 'Active|Main PID'

Mask nftables.

#systemctl mask --now nftables
#systemctl start nftables
Failed to start nftables.service: Unit nftables.service is masked.

The hello service.

/etc/systemd/system/hello.service

[Unit]
Description=Hello demo service
 
[Service]
ExecStart=/usr/bin/bash -c 'while true; do echo "hello $(date)"; sleep 60; done'
Restart=on-failure
 
[Install]
WantedBy=multi-user.target

#systemctl daemon-reload
#systemctl enable --now hello

Manage and change services

Doel

Voordat je begint

Taken

Controleer je werk

Hints

Oplossing

Mijn notities

Lessen voor dit lab

Commando's in dit lab