.\" Copyright (C) 1994, 1995, Daniel Quinlan <quinlan@yggdrasil.com>
.\" Copyright (C) 2002-2008, 2017, Michael Kerrisk <mtk.manpages@gmail.com>
.\" Copyright (C) 2023, Alejandro Colomar <alx@kernel.org>
.\"
.\" SPDX-License-Identifier: GPL-3.0-or-later
.\"
.TH proc_locks 5 2024-05-02 "Linux man-pages 6.9.1"
.SH NAME
/proc/locks \- current file locks and leases
.SH DESCRIPTION
.TP
.I /proc/locks
This file shows current file locks
(\c
.BR flock (2)
and
.BR fcntl (2))
and leases
(\c
.BR fcntl (2)).
.IP
An example of the content shown in this file is the following:
.IP
.in +4n
.EX
1: POSIX  ADVISORY  READ  5433 08:01:7864448 128 128
2: FLOCK  ADVISORY  WRITE 2001 08:01:7864554 0 EOF
3: FLOCK  ADVISORY  WRITE 1568 00:2f:32388 0 EOF
4: POSIX  ADVISORY  WRITE 699 00:16:28457 0 EOF
5: POSIX  ADVISORY  WRITE 764 00:16:21448 0 0
6: POSIX  ADVISORY  READ  3548 08:01:7867240 1 1
7: POSIX  ADVISORY  READ  3548 08:01:7865567 1826 2335
8: OFDLCK ADVISORY  WRITE \-1 08:01:8713209 128 191
.EE
.in
.IP
The fields shown in each line are as follows:
.RS
.IP [1] 5
The ordinal position of the lock in the list.
.IP [2]
The lock type.
Values that may appear here include:
.RS
.TP
.B FLOCK
This is a BSD file lock created using
.BR flock (2).
.TP
.B OFDLCK
This is an open file description (OFD) lock created using
.BR fcntl (2).
.TP
.B POSIX
This is a POSIX byte-range lock created using
.BR fcntl (2).
.RE
.IP [3]
Among the strings that can appear here are the following:
.RS
.TP
.B ADVISORY
This is an advisory lock.
.TP
.B MANDATORY
This is a mandatory lock.
.RE
.IP [4]
The type of lock.
Values that can appear here are:
.RS
.TP
.B READ
This is a POSIX or OFD read lock, or a BSD shared lock.
.TP
.B WRITE
This is a POSIX or OFD write lock, or a BSD exclusive lock.
.RE
.IP [5]
The PID of the process that owns the lock.
.IP
Because OFD locks are not owned by a single process
(since multiple processes may have file descriptors that
refer to the same open file description),
the value \-1 is displayed in this field for OFD locks.
(Before Linux 4.14,
.\" commit 9d5b86ac13c573795525ecac6ed2db39ab23e2a8
a bug meant that the PID of the process that
initially acquired the lock was displayed instead of the value \-1.)
.IP [6]
Three colon-separated subfields that identify the major and minor device
ID of the device containing the filesystem where the locked file resides,
followed by the inode number of the locked file.
.IP [7]
The byte offset of the first byte of the lock.
For BSD locks, this value is always 0.
.IP [8]
The byte offset of the last byte of the lock.
.B EOF
in this field means that the lock extends to the end of the file.
For BSD locks, the value shown is always
.IR EOF .
.RE
.IP
Since Linux 4.9,
.\" commit d67fd44f697dff293d7cdc29af929241b669affe
the list of locks shown in
.I /proc/locks
is filtered to show just the locks for the processes in the PID
namespace (see
.BR pid_namespaces (7))
for which the
.I /proc
filesystem was mounted.
(In the initial PID namespace,
there is no filtering of the records shown in this file.)
.IP
The
.BR lslocks (8)
command provides a bit more information about each lock.
.SH SEE ALSO
.BR proc (5)