man > proc_pid_fdinfo(5)

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  re‐
              ferred 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 as‐
              sociated with this file descriptor.

              For  signalfd file descriptors (see signalfd(2)), we see (since Linux 3.8) the follow‐
              ing 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 SIG‐
              INT 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  di‐
              rectory 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 follow‐
              ing 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 hexadeci‐
                     mal).

              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,  ex‐
                     pressed  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)

Linux man-pages 6.7                          2023-08-15                           proc_pid_fdinfo(5)