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NAME | DESCRIPTION | HISTORY | SEE ALSO | COLOPHON |
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proc_pid_fdinfo(5) File Formats Manual proc_pid_fdinfo(5)
/proc/pid/fdinfo/ - information about file descriptors
This is a subdirectory containing one entry for each file which
the process has open, named by its file descriptor. The files in
this directory are readable only by the owner of the process. The
contents of each file can be read to obtain information about the
corresponding file descriptor. The content depends on the type of
file referred to by the corresponding file descriptor.
For regular files and directories, we see something like:
$ cat /proc/12015/fdinfo/4
pos: 1000
flags: 01002002
mnt_id: 21
The fields are as follows:
pos This is a decimal number showing the file offset.
flags This is an octal number that displays the file access mode
and file status flags (see open(2)). If the close-on-exec
file descriptor flag is set, then flags will also include
the value O_CLOEXEC.
Before Linux 3.1, this field incorrectly displayed the
setting of O_CLOEXEC at the time the file was opened,
rather than the current setting of the close-on-exec flag.
mnt_id This field, present since Linux 3.15, is the ID of the
mount containing this file. See the description of
/proc/pid/mountinfo.
For eventfd file descriptors (see eventfd(2)), we see (since Linux
3.8) the following fields:
pos: 0
flags: 02
mnt_id: 10
eventfd-count: 40
eventfd-count is the current value of the eventfd counter, in
hexadecimal.
For epoll file descriptors (see epoll(7)), we see (since Linux
3.8) the following fields:
pos: 0
flags: 02
mnt_id: 10
tfd: 9 events: 19 data: 74253d2500000009
tfd: 7 events: 19 data: 74253d2500000007
Each of the lines beginning tfd describes one of the file
descriptors being monitored via the epoll file descriptor (see
epoll_ctl(2) for some details). The tfd field is the number of
the file descriptor. The events field is a hexadecimal mask of
the events being monitored for this file descriptor. The data
field is the data value associated with this file descriptor.
For signalfd file descriptors (see signalfd(2)), we see (since
Linux 3.8) the following fields:
pos: 0
flags: 02
mnt_id: 10
sigmask: 0000000000000006
sigmask is the hexadecimal mask of signals that are accepted via
this signalfd file descriptor. (In this example, bits 2 and 3 are
set, corresponding to the signals SIGINT and SIGQUIT; see
signal(7).)
For inotify file descriptors (see inotify(7)), we see (since Linux
3.8) the following fields:
pos: 0
flags: 00
mnt_id: 11
inotify wd:2 ino:7ef82a sdev:800001 mask:800afff ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:2af87e00220ffd73
inotify wd:1 ino:192627 sdev:800001 mask:800afff ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:27261900802dfd73
Each of the lines beginning with "inotify" displays information
about one file or directory that is being monitored. The fields
in this line are as follows:
wd A watch descriptor number (in decimal).
ino The inode number of the target file (in hexadecimal).
sdev The ID of the device where the target file resides (in
hexadecimal).
mask The mask of events being monitored for the target file (in
hexadecimal).
If the kernel was built with exportfs support, the path to the
target file is exposed as a file handle, via three hexadecimal
fields: fhandle-bytes, fhandle-type, and f_handle.
For fanotify file descriptors (see fanotify(7)), we see (since
Linux 3.8) the following fields:
pos: 0
flags: 02
mnt_id: 11
fanotify flags:0 event-flags:88002
fanotify ino:19264f sdev:800001 mflags:0 mask:1 ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:4f261900a82dfd73
The fourth line displays information defined when the fanotify
group was created via fanotify_init(2):
flags The flags argument given to fanotify_init(2) (expressed in
hexadecimal).
event-flags
The event_f_flags argument given to fanotify_init(2)
(expressed in hexadecimal).
Each additional line shown in the file contains information about
one of the marks in the fanotify group. Most of these fields are
as for inotify, except:
mflags The flags associated with the mark (expressed in
hexadecimal).
mask The events mask for this mark (expressed in hexadecimal).
ignored_mask
The mask of events that are ignored for this mark
(expressed in hexadecimal).
For details on these fields, see fanotify_mark(2).
For timerfd file descriptors (see timerfd(2)), we see (since Linux
3.17) the following fields:
pos: 0
flags: 02004002
mnt_id: 13
clockid: 0
ticks: 0
settime flags: 03
it_value: (7695568592, 640020877)
it_interval: (0, 0)
clockid
This is the numeric value of the clock ID (corresponding to
one of the CLOCK_* constants defined via <time.h>) that is
used to mark the progress of the timer (in this example, 0
is CLOCK_REALTIME).
ticks This is the number of timer expirations that have occurred,
(i.e., the value that read(2) on it would return).
settime flags
This field lists the flags with which the timerfd was last
armed (see timerfd_settime(2)), in octal (in this example,
both TFD_TIMER_ABSTIME and TFD_TIMER_CANCEL_ON_SET are
set).
it_value
This field contains the amount of time until the timer will
next expire, expressed in seconds and nanoseconds. This is
always expressed as a relative value, regardless of whether
the timer was created using the TFD_TIMER_ABSTIME flag.
it_interval
This field contains the interval of the timer, in seconds
and nanoseconds. (The it_value and it_interval fields
contain the values that timerfd_gettime(2) on this file
descriptor would return.)
Linux 2.6.22.
proc(5)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
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
Linux man-pages 6.15 2025-05-17 proc_pid_fdinfo(5)
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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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