report a snapshot of the current processes.
# man lsof
DESCRIPTION
An open file may be a regular file, a directory, a block special file, a character special file,
an executing text reference, a library, a stream or a network file (Internet socket, NFS file or UNIX domain socket.)
A specific file or all the files in a file system may be selected by path.
OPTIONS
In the absence of any options, lsof lists all open files belonging to all active processes.
-i [i] selects the listing of files any of whose Internet address matches the address specified in i.
An Internet address is specified in the form (Items in square brackets are optional.):
[46][protocol][@hostname|hostaddr][:service|port]
-a This option causes list selection options to be ANDed, as described above.
-p s This option excludes or selects the listing of files for the processes whose
optional process IDentification (PID) numbers are in the comma-separated set s - e.g., 123 or 123,^456.
(There should be no spaces in the set.)
PID numbers that begin with ^ (negation) represent exclusions.
-D D directs lsof's use of the device cache file.
-u s selects the listing of files for the user whose login names or user ID numbers
are in the comma-separated set s - e.g., ``abe'', or ``548,root''.
# lsof -i COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME systemd 1 root 45u IPv6 13815 0t0 TCP *:sunrpc (LISTEN) systemd 1 root 46u IPv4 13816 0t0 TCP *:sunrpc (LISTEN) chronyd 645 chrony 1u IPv4 14842 0t0 UDP localhost:323 chronyd 645 chrony 2u IPv6 14843 0t0 UDP localhost:323 dhclient 963 root 6u IPv4 15848 0t0 UDP *:bootpc dhclient 963 root 20u IPv4 15769 0t0 UDP *:54379 dhclient 963 root 21u IPv6 15770 0t0 UDP *:33421 vsftpd 1126 root 3u IPv6 16667 0t0 TCP *:ftp (LISTEN) xinetd 1127 root 5u IPv4 16742 0t0 UDP *:tftp httpd 1132 root 4u IPv6 17556 0t0 TCP *:http (LISTEN) httpd 1132 root 6u IPv6 17566 0t0 TCP *:https (LISTEN) ....
# lsof -i -P COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME systemd 1 root 45u IPv6 13815 0t0 TCP *:111 (LISTEN) systemd 1 root 46u IPv4 13816 0t0 TCP *:111 (LISTEN) chronyd 645 chrony 1u IPv4 14842 0t0 UDP localhost:323 chronyd 645 chrony 2u IPv6 14843 0t0 UDP localhost:323 dhclient 963 root 6u IPv4 15848 0t0 UDP *:68 dhclient 963 root 20u IPv4 15769 0t0 UDP *:54379 dhclient 963 root 21u IPv6 15770 0t0 UDP *:33421 vsftpd 1126 root 3u IPv6 16667 0t0 TCP *:21 (LISTEN) xinetd 1127 root 5u IPv4 16742 0t0 UDP *:69 httpd 1132 root 4u IPv6 17556 0t0 TCP *:80 (LISTEN) httpd 1132 root 6u IPv6 17566 0t0 TCP *:443 (LISTEN)
# lsof -i :25 COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME master 4031 root 11u IPv4 9638 TCP localhost.localdomain:smtp (LISTEN) master 4031 root 14u IPv4 9642 TCP test1.example.local:smtp (LISTEN) smtpd 25830 postfix 6u IPv4 9642 TCP test1.example.local:smtp (LISTEN) #
# lsof -i :80,443 COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME httpd 2880 root 3u IPv6 8421 TCP *:http (LISTEN) httpd 2927 apache 3u IPv6 8421 TCP *:http (LISTEN) httpd 2928 apache 3u IPv6 8421 TCP *:http (LISTEN) httpd 2929 apache 3u IPv6 8421 TCP *:http (LISTEN) httpd 2930 apache 3u IPv6 8421 TCP *:http (LISTEN) httpd 2931 apache 3u IPv6 8421 TCP *:http (LISTEN) httpd 2932 apache 3u IPv6 8421 TCP *:http (LISTEN) httpd 2936 apache 3u IPv6 8421 TCP *:http (LISTEN) httpd 2938 apache 3u IPv6 8421 TCP *:http (LISTEN) #
# lsof -p 3804 # lsof -a -p 3804
# lsof | wc -l
# lsof /path/file # lsof /var/log/httpd/access_log
# lsof -D /var/log/httpd/