How to list the open file descriptors (and the files they refer to) in my current bash session
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?
bash is not part of the kernel, so it can not know what other processes are doing, even those that it started.
@JuliePelletier: but child processes do not change the file descriptors of the parent process, do they?
5 Answers 5
Yes, this will list all open file descriptors:
$ ls -l /proc/$$/fd total 0 lrwx------ 1 isaac isaac 64 Dec 28 00:56 0 -> /dev/pts/6 lrwx------ 1 isaac isaac 64 Dec 28 00:56 1 -> /dev/pts/6 lrwx------ 1 isaac isaac 64 Dec 28 00:56 2 -> /dev/pts/6 lrwx------ 1 isaac isaac 64 Dec 28 00:56 255 -> /dev/pts/6 l-wx------ 1 isaac isaac 64 Dec 28 00:56 4 -> /home/isaac/testfile.txt Of course, as usual: 0 is stdin, 1 is stdout and 2 is stderr.
The 4th is an open file (to write) in this case.
@JZ. $$ will give the process ID of the currently running shell. Try echo $$ and ps and compare their outputs. Similar question here.
Assuming you want to list the file descriptors that are attached to any terminal, you can use lsof / fuser or similar like:
$ lsof -p $$ 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/$$/fd/ too e.g.:
Use the lsof utility to print all file descriptors for the current shell process (process identified by -p $$ ) 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:
Counting open files per process
I’m working on an application that monitors the processes’ resources and gives a periodic report in Linux, but I faced a problem in extracting the open files count per process. This takes quite a while if I take all of the files and group them according to their PID and count them. How can I take the open files count for each process in Linux?
5 Answers 5
Have a look at the /proc/ file system:
To do this for all processes, use this:
cd /proc for pid in 2* do echo "PID = $pid with $(ls /proc/$pid/fd/ | wc -l) file descriptors" done As a one-liner (filter by appending | grep -v «0 FDs» ):
for pid in /proc/3*; do printf "PID %6d has %4d FDs\n" $(basename $pid) $(ls $pid/fd | wc -l); done As a one-liner including the command name, sorted by file descriptor count in descending order (limit the results by appending | head -10 ):
for pid in /proc/2*; do p=$(basename $pid); printf "%4d FDs for PID %6d; command=%s\n" $(ls $pid/fd | wc -l) $p "$(ps -p $p -o comm=)"; done | sort -nr Credit to @Boban for this addendum:
You can pipe the output of the script above into the following script to see the ten processes (and their names) which have the most file descriptors open:
. done | sort -rn -k5 | head | while read -r _ _ pid _ fdcount _ do command=$(ps -o cmd -p "$pid" -hc) printf "pid = %5d with %4d fds: %s\n" "$pid" "$fdcount" "$command" done Here’s another approach to list the top-ten processes with the most open fds, probably less readable, so I don’t put it in front:
find /proc -maxdepth 1 -type d -name '1*' \ -exec bash -c "ls <>/fd/ | wc -l | tr '\n' ' '" \; \ -printf "fds (PID = %P), command: " \ -exec bash -c "tr '\0' ' ' < <>/cmdline" \; \ -exec echo \; | sort -rn | head Of course, you will need to have root permissions to do that for many of the processes. Their file descriptors are kind of private, you know 😉
/proc/$pid/fd lists descriptor files, that is slightly different of «open files» as we can have memory map and other unusual file objects.
This extends the answer and turns pids to command names: for pid in 7*; do echo «PID = $pid with $(ls /proc/$pid/fd/ 2>/dev/null | wc -l) file descriptors»; done | sort -rn -k5 | head | while read -r line; do pid= echo $line | awk ‘
Yeah, well. Instead of parsing the original output and then call ps again for each process to find out its command, it might make more sense to use /proc/$pid/cmdline in the first loop. While technically it is still possible for a process to disappear between the evaluating of 5* and the scanning of its disc, this is less likely.
Executing command=$(ps -o cmd -p «$pid» -hc) gave me Warning: bad syntax, perhaps a bogus ‘-‘ . It worked running as command=$(ps -o cmd -p «$pid» hc) .
ps aux | sed 1d | awk '' | xargs -I <> bash -c <> For Fedora, it gives: lsof: WARNING: can’t stat() fuse.gvfsd-fuse file system /run/user/1000/gvfs Output information may be incomplete. lsof: no pwd entry for UID 65535
I used this to find top filehandler-consuming processes for a given user (username) where dont have lsof or root access:
for pid in `ps -o pid -u username` ; do echo "$(ls /proc/$pid/fd/ 2>/dev/null | wc -l ) for PID: $pid" ; done | sort -n | tail How can I take the open files count for each process in Linux?
if you’re running it from root (e.g. prefixing the command with sudo -E env PATH=$PATH ), otherwise it’ll only return file descriptor counts per process whose /proc//fd you may list. This will give you a big JSON document/tree whose nodes look something like:
The content of fd dictionary is counts per file descriptor type. The most interesting ones are probably these (see procfile.Fd description or man fstat for more details):
I’m the author of Procpath, which is a tool that provides a nicer interface to procfs for process analysis. You can record a process tree’s procfs stats (in a SQLite database) and plot any of them later. For instance this is how my Firefox’s process tree (root PID 2468) looks like with regards to open file descriptor count (sum of all types):
procpath --logging-level ERROR record -f stat,fd -i 1 -d ff_fd.sqlite \ '$..children[?(@.stat.pid == 2468)]' # Ctrl+C procpath plot -q fd -d ff_fd.sqlite -f ff_df.svg 
If I’m interested in only a particular type of open file descriptors (say, sockets) I can plot it like this:
procpath plot --custom-value-expr fd_sock -d ff_fd.sqlite -f ff_df.svg