Linux file descriptors and open modes

Ever want to find out what modes a file was opened with originally ?

First find the file descriptor number

ls /proc//fd
Eg
ls -l /proc/32048/fd/30
l-wx------ 1 apache apache 64 Jan 18 07:15 30 -> /var/log/httpd/ntop-access_log

Then check fdinfo

cat /proc/32048/fdinfo/30
pos: 0
flags: 0102001

The flags are derived from the open system call http://linux.about.com/od/commands/l/blcmdl2_open.htm

To actually decipher the octal codes , look under /usr/include/bits/fcntl.h

If there are multiple codes, the codes are appended together.