[systemd-devel] ExecStart vs ExecStartPre
christian at iwakd.de
Tue May 26 14:26:11 PDT 2015
On 05/26/2015 11:12 PM, Steven Noonan wrote:
> Hi there,
> I'm wondering what the functional difference is between doing:
> From my read of the systemd.service man page, they appear to have the
> same behavior in the common use case.
Three differences come directly to mind:
- If you have unit of type that is NOT oneshot (simple, forking,
etc.), you can have only a single ExecStart= line, not multiple
ones. The main service process must be started in ExecStart=
and not ExecStartPre=.
- Even in Type=oneshot units you must have at least one ExecStart=
line (but can in any case have an arbitrary amount of ExecStartPre=
lines, even zero).
- If you set PermissionsStartOnly= or RootDirectoryStartOnly=, then
certain settings will be applied to ExecStart= but not to
ExecStartPre= (see manpage for details).
(There are probably more.)
Generally speaking, I follow the following guidelines when writing
- Type=oneshot: I typically use only ExecStart= and only use
ExecStartPre= if I have to use *StartOnly=true (see above).
- other types: ExecStart= to start the service proper, ExecStartPre=
for preparatory things (like generating a default config if none
is already present or something along those lines)
But it really depends on your use case and as always YMMV.
Hope that helps!
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