BUILD: introduce "--with-syslog=stderr" option

[alexey-tikhonov]

to be used in containers-like environments where
no system wide logger is available.

[ikerexxe]

LGTM. Thank you for the patch!

[aplopez]

I have just one question, otherwise I'm OK with these changes.

Shouldn't the sssd(8) man page be updated to show the loggers (--logger command line option) that are actually available, and maybe limit the accepted values? For instance, journald will not be available if SSSD is configured with --with-syslog=stderr.

[alexey-tikhonov]

Shouldn't the sssd(8) man page be updated to show the loggers (--logger command line option) that are actually available, and maybe limit the accepted values?

@aplopez, but this is unrelated to this PR.
--logger defines where DEBUG() will go.

--with-syslog= defines where sss_log() will go (and this is NOT configurable runtime).

There is indeed an issue with the man page: journald won't be available if SSSD is not built WITH_JOURNALD, but it is not introduced / not relevant to this PR. And it only affects systems where systemd-journald build deps aren't available in the buildroot.

[alexey-tikhonov]

To test this one can use a copr build from #7832 and run

# su - sssd -s /usr/bin/ -c 'sssd -i --logger=files'

This helped me to realized there is a bug actually - a new line is missing:

# su - sssd -s /usr/bin/bash -c 'sssd -i --logger=files'
Starting upStarting upStarting upStarting upStarting upStarting upStarting upFailed to initialize credentials using keytab [MEMORY:/etc/krb5.keytab]: Cannot contact any KDC for realm...

Another problem is that output is intermixed so it's difficult to understand what process output where.
I'll add a prefix, but that's not enough...

[alexey-tikhonov]

Updated.

Well, this is better:

# su - sssd -s /usr/bin/bash -c 'sssd -i --logger=files'
sssd: Starting up
be[subid.test]: Starting up
nss: Starting up
sudo: ssh: Starting up
Starting up
pam: Starting up
ifp: Starting up
pac: Starting up

but fflush() isn't enough to avoid lines intermix (as seen in this example - sudo vs ssh).

There is no trivial solution for this.

But taking into account this is an experimental feature for constrained (systemd/syslog-less) environments like single-app containers, and we aren't going to use/advertise it in Fedora/CS and other regular distributions, imo it's "good enough".

[aplopez]

Shouldn't the sssd(8) man page be updated to show the loggers (--logger command line option) that are actually available, and maybe limit the accepted values?

@aplopez, but this is unrelated to this PR. --logger defines where DEBUG() will go.

Gosh! You are right. I mixed everything.

[aplopez]

ACK
Thank you.

[ikerexxe]

LGTM!