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_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 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_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 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 -ENXIO. 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 -ENXIO (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 -ENXIO. 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 -ENXIO. 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. 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() and sd_peer_get_user_slice() 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. On success, these calls return 0 or a positive integer. On failure, these calls return a negative errno-style error code. Returned errors may indicate the following problems: -ENXIO Given field is not specified for the described process or peer. -ESRCH The specified PID does not refer to a running process. -ENOMEM Memory allocation failed. 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. systemd1, sd-login3, sd_session_is_active3, getsid2, systemd.slice5, systemd-machined.service8