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lsof is a UNIX specific tool that LiSts Open Files. Everything in Unix is a file: sockets, directories, processes, devices, pipes, etc. Because of this lsof is able to display information about current processes, network information and connections.

Description and Review

lsof was developed by Victor Abell. Written in C, its main purpose is to show information about files that are opened by running processes on the system. It shares similar functionality with netstat, but also lists the network port the service is using. This is a special tool in forensics due to the amount of information you can receive from it. It could show port redirections, sniffers, eggdrop IRC bots, or even some backdoors. The lsof command is preinstalled on most UNIX and Linux distributions. Other compressed versions of lsof can be found here.

Usage Instructions

To run lsof open a terminal and type:

lsof -n

This will display all the open files on the system. The -n option tells lsof to not do a DNS record on the IP addresses, the purpose of this is to speed up the process. The resulting output will look similar to:

COMMAND    PID       USER   FD      TYPE     DEVICE SIZE/OFF       NODE NAME init         1       root  cwd       DIR        8,1     4096          2 / init         1       root  rtd       DIR        8,1     4096          2 / init         1       root  txt       REG        8,1   190432     927934 /sbin/init init         1       root  mem       REG        8,1    47040     918484 /lib/i386-linux-gnu/ init         1       root  mem       REG        8,1    42652     918488 /lib/i386-linux-gnu/ init         1       root  mem       REG        8,1    92016     918478 /lib/i386-linux-gnu/ ksoftirqd    3       root  txt   unknown                                /proc/3/exe migration    6       root  cwd       DIR        8,1     4096          2 / migration    6       root  rtd       DIR        8,1     4096          2 / migration    6       root  txt   unknown                                /proc/6/exe watchdog/    7       root  cwd       DIR        8,1     4096          2 / watchdog/    7       root  rtd       DIR        8,1     4096          2 / watchdog/    7       root  txt   unknown                                /proc/7/exe cpuset       8       root  cwd       DIR        8,1     4096          2 / cpuset       8       root  rtd       DIR        8,1     4096          2 / cpuset       8       root  txt   unknown                                /proc/8/exe khelper      9       root  cwd       DIR        8,1     4096          2 / khelper      9       root  rtd       DIR        8,1     4096          2 / khelper      9       root  txt   unknown                                /proc/9/exe kdevtmpfs   10       root  cwd       DIR        0,5     4240          3 / kdevtmpfs   10       root  rtd       DIR        0,5     4240          3 / kdevtmpfs   10       root  txt   unknown                                /proc/10/exe netns       11       root  cwd       DIR        8,1     4096          2 / netns       11       root  rtd       DIR        8,1     4096          2 / netns       11       root  txt   unknown                                /proc/11/exe sync_supe   12       root  cwd       DIR        8,1     4096          2 /

To have lsof find all the open sockets on the system the -i option can be used

lsof -i

An example of the resulting output is:

COMMAND    PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME avahi-dae  689  avahi   12u  IPv4  14766      0t0  UDP *:mdns avahi-dae  689  avahi   13u  IPv6  14767      0t0  UDP *:mdns avahi-dae  689  avahi   14u  IPv4  14768      0t0  UDP *:54424 avahi-dae  689  avahi   15u  IPv6  14769      0t0  UDP *:39288 dnsmasq   1099 nobody    4u  IPv4  17859      0t0  UDP ubuntu:domain dnsmasq   1099 nobody    5u  IPv4  17860      0t0  TCP ubuntu:domain (LISTEN) cups-brow 3334   root    8u  IPv4  30678      0t0  UDP *:ipp dhclient  4133   root    6u  IPv4  33401      0t0  UDP *:bootpc

Lsof can also be used to view which processes are listening to a given port:

lsof -i :[port#]

To show all the TCP and UDP connections

Lsof -i tcp; lsof -i udp

To view which process opened a file

Lsof /file/path

To view all the processes that opened files in a given directory

Lsof +d /directory

To view all the processes opened by a user

Lsof -u username

To view all the files opened by a process

Lsof -p pid

See Also