'\" t
.TH "SD_PIDFD_GET_INODE_ID" "3" "" "systemd 261.1" "sd_pidfd_get_inode_id"
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.SH "NAME"
sd_pidfd_get_inode_id \- Acquire the 64\-bit inode ID of a PID file descriptor (PIDFD)
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-daemon\&.h>
.fi
.ft
.HP \w'int\ sd_pidfd_get_inode_id('u
.BI "int sd_pidfd_get_inode_id(int\ " "pidfd" ", uint64_t\ *" "ret" ");"
.SH "DESCRIPTION"
.PP
\fBsd_pidfd_get_inode_id()\fR
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\&.
.PP
As a typical example, the service manager sets
\fI$MAINPIDFDID\fR
and
\fI$MANAGERPIDFDID\fR
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\&.
.PP
On 64\-bit architectures, the inode ID can be directly obtained via a call to
\fBfstat\fR(2)
on a given pidfd\&. However, on 32\-bit architectures
struct stat\*(Aqs \&.st_ino field is also 32\-bit, which similar to PIDs is subject to reuse\&. Therefore, a second mechanism leveraging
\fBname_to_handle_at\fR(2)
has been added to kernel in v6\&.14\&. This helper is added to simplify downstream handling of pidfd/pidfs internals\&.
.SH "RETURN VALUE"
.PP
On success, the function returns 0 or a positive integer\&. On failure, a negative errno\-style error code is returned\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-EOPNOTSUPP\fR
.RS 4
The stable PIDFD inode ID is not supported by the running kernel, or the system is 32\-bit and
\fBname_to_handle_at()\fR
is unavailable\&.
.RE
.PP
\fB\-EBADF\fR
.RS 4
The specified file descriptor is invalid, or is not a PIDFD\&.
.RE
.SH "NOTES"
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.SH "HISTORY"
.PP
\fBsd_pidfd_get_inode_id()\fR
was added in version 258\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1), \fBsd-daemon\fR(3), \fBsd_notify\fR(3), \fBsystemd.exec\fR(5)