proc_pid_fdinfo(5) File Formats Manual proc_pid_fdinfo(5)
NAME
/proc/pid/fdinfo/ - information about file descriptors
DESCRIPTION
/proc/pid/fdinfo/ (since Linux 2.6.22)
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 descrip-
tor.
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 de-
scriptors 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) (ex-
pressed 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 hexadec-
imal).
mask The events mask for this mark (expressed in hexadecimal).
ignored_mask
The mask of events that are ignored for this mark (ex-
pressed 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 oc-
curred, (i.e., the value that read(2) on it would re-
turn).
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_CAN-
CEL_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_AB-
STIME 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.)
SEE ALSO
proc(5)
Linux man-pages 6.7 2023-08-15 proc_pid_fdinfo(5)
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