1. List all Open Files with lsof Command

> lsof
 COMMAND    PID      USER   FD      TYPE     DEVICE  SIZE/OFF       NODE NAME
 init         1      root  cwd      DIR      253,0      4096          2 /
 init         1      root  rtd      DIR      253,0      4096          2 /
 init         1      root  txt      REG      253,0    145180     147164 /sbin/init
 init         1      root  mem      REG      253,0   1889704     190149 /lib/libc-2.12.so

FD column stands for File Descriptor, This column values are as below:
- cwd current working directory
- rtd root directory
- txt program text (code and data)
- mem memory-mapped file


To get the count of open files you can use wc -l with lsof like as follow:

lsof | wc -l

2. List User Specific Opened Files

lsof -u alireza
 COMMAND  PID    USER   FD   TYPE     DEVICE SIZE/OFF   NODE NAME
 sshd    1838 alireza  cwd    DIR      253,0     4096      2 /
 sshd    1838 alireza  rtd    DIR      253,0     4096      2 /

#linux #sysadmin #lsof #wc #file_descriptor

I have a script that checks a source folder for new files in case there are files in the source folder, it will move those files to destination.

The problem I encountered recently was that files are huge and it may be in the middle of the copying into source by another process so my script tries to move an incomplete file to a destination. Let's say the file is 4GB in size and just only 1GB of the file has been copied. I have to wait until file is 4GB and other handler using that file, then I should safely move the file.

You can use lsof command in order to check which processes are using the source file:

if [[ `lsof -- /var/my-folder/my-big-file.tar.gz` ]]
then
     echo "File is being used by a process."
     exit 1
 fi

NOTE: you can give file directly to lsof using -- or you can use grep command as follow:

lsof | grep /var/my-folder/my-big-file.tar.gz

NOTE2: if you are in a loop use break instead of exit.

NOTE3: if you get command not found, install it using apt-get install lsof

#linux #sysadmin #lsof #grep