This will do it (in about 40 seconds on my system):
#!/bin/bash
[ "$BASHPID" = "$$" ] || { echo "Must run in a new process group"; exit 1; }>&2
cnt0() { cnt0=$#; }
cnt1() { cnt1=$#; }
tmpd=
trap 'rm -rf "$tmpd"; exit 1' INT HUP QUIT EXIT
tmpd=$(mktemp -d)
mkfifo "$tmpd/fifo"
exec 4<>"$tmpd/fifo"
rm -rf "$tmpd"
trap - INT HUP QUIT EXIT
open_all()
{
cnt0 /proc/self/fd/*;
while exec {fd}</dev/null; do :; done;
cnt1 /proc/self/fd/*;
nopened=$((cnt1-cnt0));
echo $nopened >&4;
cat /proc/sys/fs/file-nr
if ((nopened)); then
sleep 10000000
fi
}
( open_all )&
while :; do
if read nopened <&4 && ((nopened)); then
( open_all )&
continue
fi
break
done
kill -TERM -$$
It works by opening /dev/null
in a subshell as many times as possible (it should work about 1000-4000 times depending on your ulimit -n
).
If at least one filedescriptor was opened, the parent is notified via a pipe and the subshell is suspended with sleep
. The parent process responds to a sucessful fd-allocation in the child by continuing the process in another subshell until one subshell fails.
/proc/sys/fs/file-nr
is cat
ted on each iteration to let you know how the process continues.
At the end of the process, you should get something like:
...
778192 0 786806
779248 0 786806
780272 0 786806
781264 0 786806
782256 0 786806
783280 0 786806
784304 0 786806
785328 0 786806
786352 0 786806
./open_all: line 35: cannot redirect standard input from /dev/null: Too many open files in system
./open_all: line 18: fd: Too many open files in system
Terminated
One interesting thing I learned from this is that duplicated filedescriptors (from dup or fork) don't count towards the limit (spawning a process from a parent process with many filedescriptors doesn't increase the count).