Closing a File Descriptor of the Current Shell
·1 min
Table of Contents
Description #
Solving a sad server - The file /home/admin/somefile is open for writing by some process. Close this file without killing the process.
bash has the file open with a fd of 77:
admin@i-0a8158ef4cb3362f5:~$ ls
agent openfile.sh somefile
admin@i-0a8158ef4cb3362f5:~$ lsof somefile
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
bash 811 admin 77w REG 259,1 0 272875 somefile
You can think of file descriptor as “Hey Kernel! open a file and give me a number”.
The command that triggered it, is exec inside .bashrc:
admin@i-0cbfc1b45f3b71168:~$ sudo grep -irln "somefile" /* 2> /dev/null
/home/admin/.bashrc
/home/admin/agent/check.sh
/home/admin/openfile.sh
^C
admin@i-0cbfc1b45f3b71168:~$
admin@i-0cbfc1b45f3b71168:~$ cat .bashrc | grep somefile
exec 77> /home/admin/somefile
Closing the file descriptor with exec [fd]<&-:
admin@i-0a8158ef4cb3362f5:/proc/811$ ls -l fd; echo
total 0
lrwx------ 1 admin admin 64 Aug 10 12:30 0 -> /dev/pts/0
lrwx------ 1 admin admin 64 Aug 10 12:30 1 -> /dev/pts/0
lrwx------ 1 admin admin 64 Aug 10 12:30 2 -> /dev/pts/0
lrwx------ 1 admin admin 64 Aug 10 12:30 255 -> /dev/pts/0
l-wx------ 1 admin admin 64 Aug 10 12:30 77 -> /home/admin/somefile
admin@i-0a8158ef4cb3362f5:/proc/811$
admin@i-0a8158ef4cb3362f5:/proc/811$ exec 77<&-
lsof should return nothing:
admin@i-0a8158ef4cb3362f5:/proc/811$ cd ; lsof somefile
admin@i-0a8158ef4cb3362f5:~$
Ref #
In their own eyes they flatter themselves too much to detect or hate their sin.
– Psalms 36:2