Checking For Open Files Using 'lsof'

In order to see which files (and sockets) a given process holds open, one may use the 'lsof' command, as follows:

 # lsof -p 910
 COMMAND  PID USER  FD  TYPE DEVICE    SIZE  NODE NAME
 sendmail 910 root cwd   DIR        3,3    4096 40872 /usr/var/spool/mqueue
 sendmail 910 root rtd   DIR        3,2    1024     2 /
 sendmail 910 root txt   REG        3,3  299364 97622 /usr/sbin/sendmail
 sendmail 910 root mem   REG        3,2  342206  8082 /lib/ld-2.1.1.so
 sendmail 910 root mem   REG        3,2  219002  8118 /lib/libdb1-2.1.1.so
 sendmail 910 root mem   REG        3,2  164797  8161 /lib/libresolv-2.1.1.so
 sendmail 910 root mem   REG        3,2  364235  8125 /lib/libnsl-2.1.1.so
 sendmail 910 root mem   REG        3,2 4016683  8114 /lib/libc-2.1.1.so
 sendmail 910 root mem   REG        3,2  243964  8144 /lib/libnss_files-2.1.1.so
 sendmail 910 root mem   REG        3,2  251436  8150 /lib/libnss_nisplus-2.1.1.so
 sendmail 910 root mem   REG        3,2  251787  8148 /lib/libnss_nis-2.1.1.so
 sendmail 910 root mem   REG        3,2   65996  8142 /lib/libnss_dns-2.1.1.so
 sendmail 910 root   0r  CHR        1,3          1997 /dev/null
 sendmail 910 root   1w  CHR        1,3          1997 /dev/null
 sendmail 910 root   2w  CHR        1,3          1997 /dev/null
 sendmail 910 root   3u inet       1408           TCP *:smtp (LISTEN)
 sendmail 910 root   4u unix 0xc13b4140          1402 socket

We can see the executable file itself, the shared libraries used by the process, normal file descriptors, a TCP socket open for listening, etc.