Commit f1d8c162 authored by Cyrill Gorcunov's avatar Cyrill Gorcunov Committed by Linus Torvalds
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docs: add documentation about /proc/<pid>/fdinfo/<fd> output

[ tweak documentation]
Signed-off-by: default avatarCyrill Gorcunov <>
Cc: Pavel Emelyanov <>
Cc: Oleg Nesterov <>
Cc: Andrey Vagin <>
Cc: Al Viro <>
Cc: Alexey Dobriyan <>
Cc: James Bottomley <>
Cc: "Aneesh Kumar K.V" <>
Cc: Alexey Dobriyan <>
Cc: Matthew Helsley <>
Cc: "J. Bruce Fields" <>
Cc: "Aneesh Kumar K.V" <>
Cc: Tvrtko Ursulin <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent be77196b
......@@ -41,6 +41,7 @@ Table of Contents
3.5 /proc/<pid>/mountinfo - Information about mounts
3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
3.7 /proc/<pid>/task/<tid>/children - Information about task children
3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
4 Configuring procfs
4.1 Mount options
......@@ -1633,6 +1634,87 @@ pids, so one need to either stop or freeze processes being inspected
if precise results are needed.
3.7 /proc/<pid>/fdinfo/<fd> - Information about opened file
This file provides information associated with an opened file. The regular
files have at least two fields -- 'pos' and 'flags'. The 'pos' represents
the current offset of the opened file in decimal form [see lseek(2) for
details] and 'flags' denotes the octal O_xxx mask the file has been
created with [see open(2) for details].
A typical output is
pos: 0
flags: 0100002
The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
pair provide additional information particular to the objects they represent.
Eventfd files
pos: 0
flags: 04002
eventfd-count: 5a
where 'eventfd-count' is hex value of a counter.
Signalfd files
pos: 0
flags: 04002
sigmask: 0000000000000200
where 'sigmask' is hex value of the signal mask associated
with a file.
Epoll files
pos: 0
flags: 02
tfd: 5 events: 1d data: ffffffffffffffff
where 'tfd' is a target file descriptor number in decimal form,
'events' is events mask being watched and the 'data' is data
associated with a target [see epoll(7) for more details].
Fsnotify files
For inotify files the format is the following
pos: 0
flags: 02000000
inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
where 'wd' is a watch descriptor in decimal form, ie a target file
descriptor number, 'ino' and 'sdev' are inode and device where the
target file resides and the 'mask' is the mask of events, all in hex
form [see inotify(7) for more details].
If the kernel was built with exportfs support, the path to the target
file is encoded as a file handle. The file handle is provided by three
fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
If the kernel is built without exportfs support the file handle won't be
printed out.
For fanotify files the format is
pos: 0
flags: 02
fanotify ino:2 sdev:800013 mask:1 ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:0200000000000000
pos: 0
flags: 02
fanotify mnt_id:13 mask:1 ignored_mask:40000000
where 'ino', 'sdev' are target inode and device, 'mnt_id' is the mount
point identifier, 'mask' is the events mask used and 'ignored_mask' is
the mask of events which are to be ignored. All in hex format.
Configuring procfs
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