I am checking process file descriptor limit using :-

count = lsof <pid> | wc -l

and then finding the usage% by count/soft_limit*100

where soft_limit is found using

cat /proc/<pid>/limits
Limit Soft Limit Hard Limit Units

Max core file size 0 unlimited bytes
Max resident set unlimited unlimited bytes
Max processes 131072 131072 processes
Max open files 8000 8000 files
Max locked memory 65536 65536 bytes


So, my doubt is whether above command gives Max limit of open files or any other way to get it i.e which lsof lists

lsof lists open files and I do not believe it will operate with the argument of a PID as you've shown, check the manual page for it. Basically IMHO it will list all open files belonging to all processes unless you specify options to reduce that to be "per a user", or "per type", and not sure if PID is an option for it, but maybe it is, just not how you've shown the command above.

Therefore, "/proc/<pid>/limits" is correct. Also you can use "ulimit -a" to get a more brief report on what your process limits are.

This just exploration, or you looking for a particular reason? And the reason I'm asking is because this either matters for your knowledge, a script, or a program; and there are different methods if you're programming. For instance there are setrlimit(), getrlimit(), and prlimit() for a C/C++ program. However if you're in a script then you'd use the limits file which applies to your process ID, or the one you care to check out.