---
name: "proc_pid_fdinfo"
section: "5"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/proc_pid_fdinfo"
---

# proc\_pid\_fdinfo(5)

information about file descriptors

## NAME

/proc/pid/fdinfo/ - information about file descriptors

## DESCRIPTION

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
ino:    63107
```

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)](/open/2.md)). 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 decimal ID of the mount containing this file. See the description of */proc/*pid*/mountinfo*.

- *ino*

  This field, present since Linux 5.14, is the decimal inode number of the file.

For eventfd file descriptors (see [**eventfd**(2)](/eventfd/2.md)), we see (since Linux 3.8) the following fields:

```
pos:    0
flags:  02
mnt_id: 10
ino:    63107
eventfd-count:               40
```

*eventfd-count* is the current value of the eventfd counter, in hexadecimal.

For epoll file descriptors (see [**epoll**(7)](/epoll/7.md)), we see (since Linux 3.8) the following fields:

```
pos:    0
flags:  02
mnt_id: 10
ino:    63107
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)](/epoll_ctl/2.md) 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)](/signalfd/2.md)), we see (since Linux 3.8) the following fields:

```
pos:    0
flags:  02
mnt_id: 10
ino:    63107
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)](/signal/7.md).)

For inotify file descriptors (see [**inotify**(7)](/inotify/7.md)), we see (since Linux 3.8) the following fields:

```
pos:    0
flags:  00
mnt_id: 11
ino:    63107
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)](/fanotify/7.md)), we see (since Linux 3.8) the following fields:

```
pos:    0
flags:  02
mnt_id: 11
ino:    63107
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)](/fanotify_init/2.md):

- *flags*

  The *flags* argument given to [**fanotify\_init**(2)](/fanotify_init/2.md) (expressed in hexadecimal).

- *event-flags*

  The *event\_f\_flags* argument given to [**fanotify\_init**(2)](/fanotify_init/2.md) (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)](/fanotify_mark/2.md).

For timerfd file descriptors (see [**timerfd**(2)](/timerfd/2.md)), we see (since Linux 3.17) the following fields:

```
pos:    0
flags:  02004002
mnt_id: 13
ino:    63107
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)](/read/2.md) on it would return).

- *settime flags*

  This field lists the flags with which the timerfd was last armed (see [**timerfd\_settime**(2)](/timerfd_settime/2.md)), 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)](/timerfd_gettime/2.md) on this file descriptor would return.)

## HISTORY

Linux 2.6.22.

## SEE ALSO

[**proc**(5)](/proc/5.md)