by: adminPosted on:

Why forking is used in a unit file of a service?

My nginx unitfile is following,

[root@arif ~]# cat /usr/lib/systemd/system/nginx.service
[Unit]
Description=The nginx HTTP and reverse proxy server
After=network.target remote-fs.target nss-lookup.target

[Service]
Type=forking
PIDFile=/run/nginx.pid
# Nginx will fail to start if /run/nginx.pid already exists but has the wrong
# SELinux context. This might happen when running `nginx -t` from the cmdline.
# https://bugzilla.redhat.com/show_bug.cgi?id=1268621
ExecStartPre=/usr/bin/rm -f /run/nginx.pid
ExecStartPre=/usr/sbin/nginx -t
ExecStart=/usr/sbin/nginx
ExecReload=/bin/kill -s HUP $MAINPID
KillSignal=SIGQUIT
TimeoutStopSec=5
KillMode=process
PrivateTmp=true

[Install]
WantedBy=multi-user.target

Here, in the [Service] portion, the value of Type is equal to forking which means from here,

The process started with ExecStart spawns a child process that becomes the main process of the service. The parent process exits when the startup is complete.

My questions are,

  • Why a service does that?
  • What are the advantages for doing this?
  • What’s wrong is Type=simple or other similar options?