sd_pid_get_session
systemd
Developer
Lennart
Poettering
lennart@poettering.net
sd_pid_get_session
3
sd_pid_get_session
sd_pid_get_unit
sd_pid_get_user_unit
sd_pid_get_owner_uid
sd_pid_get_machine_name
sd_pid_get_slice
sd_pid_get_user_slice
sd_pid_get_cgroup
sd_peer_get_session
sd_peer_get_unit
sd_peer_get_user_unit
sd_peer_get_owner_uid
sd_peer_get_machine_name
sd_peer_get_slice
sd_peer_get_user_slice
sd_peer_get_cgroup
Determine session, unit, owner of a session,
container/VM or slice of a specific PID or socket
peer
#include <systemd/sd-login.h>
int sd_pid_get_session
pid_t pid
char **session
int sd_pid_get_unit
pid_t pid
char **unit
int sd_pid_get_user_unit
pid_t pid
char **unit
int sd_pid_get_owner_uid
pid_t pid
uid_t *uid
int sd_pid_get_machine_name
pid_t pid
char **name
int sd_pid_get_slice
pid_t pid
char **slice
int sd_pid_get_user_slice
pid_t pid
char **slice
int sd_pid_get_cgroup
pid_t pid
char **cgroup
int sd_peer_get_session
int fd
char **session
int sd_peer_get_unit
int fd
char **unit
int sd_peer_get_user_unit
int fd
char **unit
int sd_peer_get_owner_uid
int fd
uid_t *uid
int sd_peer_get_machine_name
int fd
char **name
int sd_peer_get_slice
int fd
char **slice
int sd_peer_get_user_slice
int fd
char **slice
int sd_peer_get_cgroup
int fd
char **cgroup
Description
sd_pid_get_session() may be used to
determine the login session identifier of a process identified by
the specified process identifier. The session identifier is a
short string, suitable for usage in file system paths. Note that
not all processes are part of a login session (e.g. system service
processes, user processes that are shared between multiple
sessions of the same user, or kernel threads). For processes not
being part of a login session this function will fail with
-ENODATA. The returned string needs to be freed with the libc
free3
call after use.
sd_pid_get_unit() may be used to
determine the systemd system unit (i.e. system service or scope
unit) identifier of a process identified by the specified PID. The
unit name is a short string, suitable for usage in file system
paths. Note that not all processes are part of a system
unit/service (e.g. user processes, or kernel threads). For
processes not being part of a systemd system unit this function
will fail with -ENODATA (More specifically: this call will not
work for kernel threads.) The returned string needs to be freed
with the libc free3
call after use.
sd_pid_get_user_unit() may be used to
determine the systemd user unit (i.e. user service or scope unit)
identifier of a process identified by the specified PID. This is
similar to sd_pid_get_unit() but applies to
user units instead of system units.
sd_pid_get_owner_uid() may be used to
determine the Unix UID (user identifier) of the owner of the
session of a process identified the specified PID. Note that this
function will succeed for user processes which are shared between
multiple login sessions of the same user, where
sd_pid_get_session() will fail. For processes
not being part of a login session and not being a shared process
of a user this function will fail with -ENODATA.
sd_pid_get_machine_name() may be used
to determine the name of the VM or container is a member of. The
machine name is a short string, suitable for usage in file system
paths. The returned string needs to be freed with the libc
free3
call after use. For processes not part of a VM or containers this
function fails with -ENODATA.
sd_pid_get_slice() may be used to
determine the slice unit the process is a member of. See
systemd.slice5
for details about slices. The returned string needs to be freed
with the libc
free3
call after use.
Similar, sd_pid_get_user_slice()
returns the user slice (as managed by the user's systemd instance)
of a process.
sd_pid_get_cgroup() returns the control
group path of the specified process, relative to the root of the
hierarchy. Returns the path without trailing slash, except for
processes located in the root control group, where "/" is
returned. To find the actual control group path in the file system
the returned path needs to be prefixed with
/sys/fs/cgroup/ (if the unified control group
setup is used), or
/sys/fs/cgroup/HIERARCHY/
(if the legacy multi-hierarchy control group setup is used).
If the pid parameter of any of these
functions is passed as 0, the operation is executed for the
calling process.
The sd_peer_get_session(),
sd_peer_get_unit(),
sd_peer_get_user_unit(),
sd_peer_get_owner_uid(),
sd_peer_get_machine_name(),
sd_peer_get_slice(),
sd_peer_get_user_slice() and
sd_peer_get_cgroup() calls operate similar to
their PID counterparts, but operate on a connected AF_UNIX socket
and retrieve information about the connected peer process. Note
that these fields are retrieved via /proc,
and hence are not suitable for authorization purposes, as they are
subject to races.
Return Value
On success, these calls return 0 or a positive integer. On
failure, these calls return a negative errno-style error
code.
Errors
Returned errors may indicate the following problems:
-ESRCH
The specified PID does not refer to a running
process.
-BADF
The specified socket file descriptor was
invalid.
-ENODATA
Given field is not specified for the described
process or peer.
-EINVAL
An input parameter was invalid (out of range,
or NULL, where that's not accepted).
-ENOMEM
Memory allocation failed.
Notes
The sd_pid_get_session(),
sd_pid_get_unit(),
sd_pid_get_user_unit(),
sd_pid_get_owner_uid(),
sd_pid_get_machine_name(),
sd_pid_get_slice(),
sd_pid_get_user_slice(),
sd_peer_get_session(),
sd_peer_get_unit(),
sd_peer_get_user_unit(),
sd_peer_get_owner_uid(),
sd_peer_get_machine_name(),
sd_peer_get_slice() and
sd_peer_get_user_slice() interfaces are
available as a shared library, which can be compiled and linked to
with the libsystemd pkg-config1
file.
Note that the login session identifier as
returned by sd_pid_get_session()
is completely unrelated to the process session
identifier as returned by
getsid2.
See Also
systemd1,
sd-login3,
sd_session_is_active3,
getsid2,
systemd.slice5,
systemd-machined.service8