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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 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.)
SEE ALSO
proc(5)