How to list the open file descriptors (and the files they refer to) in my current bash session

Question

I am running in an interactive bash session. I have created some file descriptors, using exec, and I would like to list what is the current status of my bash session.

Is there a way to list the currently open file descriptors?

@Kamaraj thanks. So bash has no built-in to do that? I need to use linux-specific features? — blueFast, Dec 28 '16 at 04:57
bash is not part of the kernel, so it can not know what other processes are doing, even those that it started. — Julie Pelletier, Dec 28 '16 at 04:58
@JuliePelletier: but child processes do not change the file descriptors of the parent process, do they? — blueFast, Dec 28 '16 at 05:09
hi, what do you mean by "I have created some file descriptors, using exec"? — Chan Kim, Feb 19 '21 at 01:53

score 91 · Accepted Answer · 2022-06-08T16:50:08.827

91

Yes, this will list all open file descriptors:

$ ls -l /proc/$$/fd
total 0
lrwx------ 1 isaac isaac 64 Dec 28 00:56 0 -> /dev/pts/6
lrwx------ 1 isaac isaac 64 Dec 28 00:56 1 -> /dev/pts/6
lrwx------ 1 isaac isaac 64 Dec 28 00:56 2 -> /dev/pts/6
lrwx------ 1 isaac isaac 64 Dec 28 00:56 255 -> /dev/pts/6
l-wx------ 1 isaac isaac 64 Dec 28 00:56 4 -> /home/isaac/testfile.txt

Of course, as usual: 0 is stdin, 1 is stdout and 2 is stderr.
The 4th is an open file (to write) in this case.

edited Jun 08 '22 at 16:50

answered Dec 28 '16 at 04:59

3

what is /proc/$$ ? specifically how does "$$" work? – JZ. Mar 02 '20 at 17:14
5

@JZ.$$ will give the process ID of the currently running shell. Try echo $$ and ps and compare their outputs. Similar question here. – ManSamVampire May 23 '20 at 18:40

score 15 · Answer 2 · answered Aug 14 '18 at 07:15

15

lsof -a -p $$

Network fd only:

lsof -i -a -p $$

answered Aug 14 '18 at 07:15

g10guang

259

score 10 · Answer 3 · answered Dec 28 '16 at 04:59

10

Assuming you want to list the file descriptors that are attached to any terminal, you can use lsof/fuser or similar like:

$ lsof -p $$ 2>/dev/null | awk '$NF ~ /\/pts\//'
bash    32406 foobar    0u   CHR 136,31      0t0      34 /dev/pts/31
bash    32406 foobar    1u   CHR 136,31      0t0      34 /dev/pts/31
bash    32406 foobar    2u   CHR 136,31      0t0      34 /dev/pts/31
bash    32406 foobar    3u   CHR 136,31      0t0      34 /dev/pts/31
bash    32406 foobar  255u   CHR 136,31      0t0      34 /dev/pts/31

These tools basically parse /proc, so you can just access /proc/$$/fd/ too e.g.:

ls /proc/$$/fd/*

answered Dec 28 '16 at 04:59

heemayl

56,300

4

The selection of \/pts\/ rejects open files like exec 4>testfile.txt – Dec 28 '16 at 05:03
@sorontar Yep, like i said this one is only for listing the ones attached to any terminal. – heemayl Dec 28 '16 at 05:06
ls /proc/$$/fd/* doesn't work for me. I get ls: /proc/48855/fd: No such file or directory :( – Christopher King May 19 '21 at 22:48

score 5 · Answer 4 · answered Dec 01 '20 at 21:36

Use the lsof utility to print all file descriptors for the current shell process (process identified by -p $$) and (-a) where the file descriptor is numeric (-d 0-256):

$ lsof -p $$ -a -d 0-256
COMMAND   PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
bash    16883  ant    0u   CHR 136,15      0t0   18 /dev/pts/15
bash    16883  ant    1u   CHR 136,15      0t0   18 /dev/pts/15
bash    16883  ant    2u   CHR 136,15      0t0   18 /dev/pts/15
bash    16883  ant  255u   CHR 136,15      0t0   18 /dev/pts/15

Pipe into Awk to print only the file descriptor and its corresponding filename:

$ lsof -p $$ -a -d 0-256  | awk '{ printf("%4s:\t%s\n", $4, $NF) }'
  FD:   NAME
  0u:   /dev/pts/15
  1u:   /dev/pts/15
  2u:   /dev/pts/15
255u:   /dev/pts/15

Note: when lsof prints the file descriptors, it appends the following code to indicate the file access mode:

r – read access
w – write access
u – read and write access

score 1 · Answer 5 · edited Apr 15 '22 at 18:54

1

If you happen to want a graphical solution, gnome-system-monitor allows you to see the opened file descriptors of a process. Right click on any process opens a contextual menu, then you can click Open Files. Or you can just select the process and press CTRL+O.

Bonus: There is also an option in the sandwich menu to search opened files by filename

edited Apr 15 '22 at 18:54

Greenonline

1,851
7
17
23

answered Apr 15 '22 at 09:28

cassepipe

180

How to list the open file descriptors (and the files they refer to) in my current bash session

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