On Wed, Aug 17, 2022 at 5:05 AM Peter Hoeg <pe...@hoeg.com> wrote: > > Hi all, > > I have a small program that queries an external web API, massages the data > and passes it off to something else. As I only need it to run during > certain windows and I didn't want to have to bother with making sure it was > alive, I am starting it using a systemd timer which is sufficiently > flexible. All good and it's super nice to be able to "outsource" all that > to systemd. > > My question is - what is the canonical way to detect that I'm running > under systemd so that I can adjust accordingly? Currently I'm checking for > the existence of the "_SYSTEMD_INVOCATION_ID" environment variable in order > to change the logging function as the default logger includes a timestamp > which is redundant when journald is picking it up. > > I'm also using LoadCredential for passing tokens but that just comes down > to looking for the right file name where the CREDENTIALS_DIRECTORY variable > points, so that really isn't systemd specific and there is a fallback in > case that isn't set or the directory/file doesn't exist anyway. > > I could of course also add a --systemd flag that toggles this but if I can > do "TheRightThing(tm)" out of the box, why not. >
What *is* specific to systemd that you need to check for and how would that change the program's behavior? It sounds to me that being started by pid1 is irrelevant here – if you want to alter your logging, then you want to check specifically whether stderr is tied to the journal, for which you can use JOURNAL_STREAM (like in https://github.com/systemd/systemd/blob/main/src/basic/log.c#L217). (In addition to disabling the timestamps you should *at least* add message priority indicators as well, either by using SyslogLevelPrefix=, or by avoiding stderr entirely and using the syslog() API for logging – if not going all the way with sd_journal_send*().) -- Mantas Mikulėnas
