[systemd-devel] journal handling of process title changes

[Patrick Donnelly]

It seems the journal is reading from /proc/pid/cmdline (argv[0]) for
each entry. So when reading using journalctl, we don't see process
title changes properly. See the below example:

#include <sys/prctl.h>
#include <systemd/sd-journal.h>

int main (int argc, char *argv[])
{
    printf("%d\n", prctl(PR_SET_NAME, "foo", 0, 0, 0));
    sd_journal_print(LOG_INFO, "hi");
    strcpy(argv[0], "abc");
    sd_journal_print(LOG_INFO, "bye2");
    return 0;
}

gcc test.c -o a.out -lsystemd
./a.out

we see:

... a.out[10321]: hi
... a.out[10321]: bye
... c[10321]: bye2

I don't see how after a cursory glance at the code, but systemd is
also magically remembering the "old" beginning of argv[0]. So, even if
I change argv[0], I must start my changes from the beginning of the
basename of the old title. So in the above example, "ab" replaced "./"
in argv[0], only "c" is printed in the log.

It seems to me systemd should be using /proc/pid/comm for this.

-- 
Patrick Donnelly