[systemd-devel] Systemd sessionid like `c508`

[Mantas Mikulėnas]

The sessions listed in loginctl are created and their IDs assigned by
systemd-logind (when asked by pam_systemd).

If /proc/*/loginuid and /proc/*/sessionid are available (set up by
pam_loginuid), then logind directly takes the audit session ID as logind
session ID.

If those are not available (kernel audit support disabled), then logind
itself allocates a logind session ID and adds the "c" prefix to prevent
collisions with audit IDs.

src/login/logind-dbus.c:870:                        if (asprintf(&id,
"c%lu", ++m->session_counter) < 0)

On Wed, Jan 11, 2023, 05:58 hai wu <haiwu.us at gmail.com> wrote:

> Where is the systemd sessionid like `c508` being generated? If kernel
> auditd is disabled, then it seems systemd `loginctl list-sessions`
> command would list user session ids all with `c` character prefix
> instead.
>
> I could not find the source code where these session ids got
> generated. Are these session ids generated from systemd source code or
> from Linux kernel source code?
>
> systemd has this function `sd_pid_get_session` to get session id, it
> seems that's parsing `/proc/self/cgroup`, instead of generating such
> session ids..
>
> Regards,
> Hai
>
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