SD_PIDFD_GET_INODE_ID(3)     sd_pidfd_get_inode_id    SD_PIDFD_GET_INODE_ID(3)

NAME
       sd_pidfd_get_inode_id - Acquire the 64-bit inode ID of a PID file
       descriptor (PIDFD)

SYNOPSIS
       #include <systemd/sd-daemon.h>

       int sd_pidfd_get_inode_id(int pidfd, uint64_t *ret);

DESCRIPTION
       sd_pidfd_get_inode_id() may be invoked to acquire the 64-bit inode ID
       of a PID file descriptor (PIDFD), which can be used to reliably
       identify a process for the current boot.

       As a typical example, the service manager sets $MAINPIDFDID and
       $MANAGERPIDFDID environment variables to the inode IDs of the service
       main process and the service manager itself, respectively, if such
       functionality is supported by the kernel.

       On 64-bit architectures, the inode ID can be directly obtained via a
       call to fstat(2) on a given pidfd. However, on 32-bit architectures
       struct stat's .st_ino field is also 32-bit, which similar to PIDs is
       subject to reuse. Therefore, a second mechanism leveraging
       name_to_handle_at(2) has been added to kernel in v6.14. This helper is
       added to simplify downstream handling of pidfd/pidfs internals.

RETURN VALUE
       On success, the function returns 0 or a positive integer. On failure, a
       negative errno-style error code is returned.

   Errors
       Returned errors may indicate the following problems:

       -EOPNOTSUPP
           The stable PIDFD inode ID is not supported by the running kernel,
           or the system is 32-bit and name_to_handle_at() is unavailable.

       -EBADF
           The specified file descriptor is invalid, or is not a PIDFD.

NOTES
       Functions described here are available as a shared library, which can
       be compiled against and linked to with the libsystemd pkg-config(1)
       file.

HISTORY
       sd_pidfd_get_inode_id() was added in version 258.

SEE ALSO
       systemd(1), sd-daemon(3), sd_notify(3), systemd.exec(5)

systemd 258                                           SD_PIDFD_GET_INODE_ID(3)