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 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, whereas 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. Similarly, 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. 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: -ESRCH The specified PID does not refer to a running process. -EBADF The specified socket file descriptor was invalid. -ENODATA The given field is not specified for the described process or peer. -EINVAL An input parameter was invalid (out of range, or NULL, where that is not accepted). -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 libelogind 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