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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_PIDFD_GET_INODE_ID(3) sd_pidfd_get_inode_id SD_PIDFD_GET_INODE_ID(3)
sd_pidfd_get_inode_id - Acquire the 64-bit inode ID of a PID file
descriptor (PIDFD)
#include <systemd/sd-daemon.h>
int sd_pidfd_get_inode_id(int pidfd, uint64_t *ret);
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.
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.
Functions described here are available as a shared library, which
can be compiled against and linked to with the
libsystemd pkg-config(1) file.
sd_pidfd_get_inode_id() was added in version 258.
systemd(1), sd-daemon(3), sd_notify(3), systemd.exec(5)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 SD_PIDFD_GET_INODE_ID(3)
Pages that refer to this page: sd-daemon(3), sd_notify(3), systemd.directives(7), systemd.index(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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