How to List Open Files with lsof
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Introduction
lsof was created by Victor A. Abell and is a utility that lists open files. Everything in Linux can be considered a file. This means that lsof can gather information on the majority of activity on your Linode, including network interfaces and network connections. lsof by default outputs a list of all open files and the processes that opened them.
There are two main drawbacks of lsof. First, it can only display information about the local machine (localhost). And second, it requires administrative privileges to print all available data. Additionally, you usually do not execute lsof without any command line parameters because it outputs a large amount of data that can be difficult to parse. This happens because lsof natively lists all open files belonging to all active processes. For example, the output of wc(1) (a word count utility) when applied to lsof on a test instance shows the size of the output is extremely large:
sudo lsof | wc
7332 68337 1058393Before You Begin
lsof without root privileges only returns the results available to the current user. If you are not familiar with the sudo command, see the
Users and Groups guide.On most major distributions, lsof comes pre-installed and you can begin using it immediately. If for any reason it is not found, you can install lsof using your preferred package manager.
Command Line Options
The lsof(8) binary supports a large number of command line options, including the following:
| Option | Description |
|---|---|
-h and -? | Both options present a help screen. Please note that you need to properly escape the ? character for -? to work. |
-a | This option tells lsof to logically ADD all provided options. |
-b | This option tells lsof to avoid kernel functions that might block the returning of results. This is a very specialized option. |
-l | If converting a user ID to a login name is working improperly or slowly, you can disable it using the -l parameter. |
–P | The -P option prevents the conversion of port numbers to port names for network files. |
-u list | The -u option allows you to define a list of login names or user ID numbers whose files are returned. The -u option supports the ^ character for excluding the matches from the output. |
-c list | The -c option selects the listing of files for processes executing the commands that begin with the characters in the list. This supports regular expressions, and also supports the ^ character for excluding the matches from the output. |
-p list | The -p option allows you to select the files for the processes whose process IDs are in the list. The -p option supports the ^ character for excluding the matches from the output. |
-g list | The -g option allows you to select the files for the processes whose optional process group IDs are in the list. The -g option supports the ^ character for excluding the matches from the output. |
-s | The -s option allows you to select the network protocols and states that interest you. The -s option supports the ^ character for excluding the matches from the output. The correct form is PROCOTCOL:STATE. Possible protocols are UDP and TCP. Some possible TCP states are: CLOSED, SYN-SENT, SYN-RECEIVED, ESTABLISHED, CLOSE-WAIT, LAST-ACK, FIN-WAIT-1, FIN-WAIT-2, CLOSING, and TIME-WAIT. Possible UDP states are Unbound and Idle. |
+d s | The +d option tells lsof to search for all open instances of directory s and the files and directories it contains at its top level. |
+D directory | The +D option tells lsof to search for all open instances of directory directory and all the files and directories it contains to its complete depth. |
-d list | The -d option specifies the list of file descriptors to include or exclude from the output. -d 1,^2 means include file descriptor 1 and exclude file descriptor 2. |
-i4 | This option is used for displaying IPv4 data only. |
-i6 | This option is used for displaying IPv6 data only. |
-i | The -i option without any values tells lsof to display network connections only. |
-i ADDRESS | The -i option with a value limits the displayed information to match that value. Some example values are TCP:25 for displaying TCP data that listens to port number 25, @google.com for displaying information related to google.com, :25 for displaying information related to port number 25, :POP3 for displaying information related to the port number that is associated to POP3 in the /etc/services file, etc. You can also combine hostnames and IP Addresses with port numbers and protocols. |
-t | The -t option tells lsof to display process identifiers without a header line. This is particularly useful for feeding the output of lsof to the kill(1) command or to a script. Notice that -t automatically selects the -w option. |
-w | The -w option disables the suppression of warning messages. |
+w | The +w option enables the suppression of warning messages. |
-r TIME | The -r option causes the lsof command to repeat every TIME seconds until the command is manually terminated with an interrupt. |
+r TIME | The +r command, with the + prefix, acts the same as the -r command, but exits its loop when it fails to find any open files. |
-n | The -n option prevents network numbers from being converted to host names. |
-F CHARACTER | The -F command instructs lsof to produce output that is suitable as input for other programs. For a complete explanation, consult the lsof manual entry. |
By default, the output of lsof includes the output of each one of its command line options, like a big logical expression with multiple OR logical operators between all the command line options. However, this default behavior can change with the use of the -a option. | |
For the full list of command line options supported by |
Anatomy of lsof Output
The following command uses the -i option to display all open UDP files/connections:
sudo lsof -i UDP
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
rpcbind 660 root 6u IPv4 20296 0t0 UDP *:sunrpc
rpcbind 660 root 7u IPv4 20298 0t0 UDP *:836
rpcbind 660 root 9u IPv6 20300 0t0 UDP *:sunrpc
rpcbind 660 root 10u IPv6 20301 0t0 UDP *:836
avahi-dae 669 avahi 12u IPv4 20732 0t0 UDP *:mdns
avahi-dae 669 avahi 13u IPv6 20733 0t0 UDP *:mdns
avahi-dae 669 avahi 14u IPv4 20734 0t0 UDP *:54087
avahi-dae 669 avahi 15u IPv6 20735 0t0 UDP *:48582
rsyslogd 675 root 6u IPv4 20973 0t0 UDP 17-5-7-8.ip.linodeusercontent.com:syslog
dhclient 797 root 6u IPv4 21828 0t0 UDP *:bootpc
ntpd 848 ntp 16u IPv6 22807 0t0 UDP *:ntp
ntpd 848 ntp 17u IPv4 22810 0t0 UDP *:ntp
ntpd 848 ntp 18u IPv4 22814 0t0 UDP localhost:ntp
ntpd 848 ntp 19u IPv4 22816 0t0 UDP 17-5-7-8.ip.linodeusercontent.com:ntp
ntpd 848 ntp 20u IPv6 22818 0t0 UDP localhost:ntp
ntpd 848 ntp 24u IPv6 24916 0t0 UDP [2a01:7e00::f03c:91ff:fe69:1381]:ntp
ntpd 848 ntp 25u IPv6 24918 0t0 UDP [fe80::f03c:91ff:fe69:1381]:ntpThe output of lsof has various columns.
- The
COMMANDcolumn contains the first nine characters of the name of the UNIX command associated with the process. - The
PIDcolumn shows the process ID of the command. - The
USERcolumn displays the name of the user that owns the process. - The
TIDcolumn shows the task ID. A blankTIDindicates a process. Note that this column does not appear in the output of manylsofcommands. - The
FDcolumn stands for file descriptor. Its values can becwd,txt,mem, andmmap. - The
TYPEcolumn displays the type of the file: regular file, directory, socket, etc. - The
DEVICEcolumn contains the device numbers separated by commas. - The value of the
SIZE/OFFcolumn is the size of the file or the file offset in bytes. The value of theNODEcolumn is the node number of a local file. - Lastly, the
NAMEcolumn shows the name of the mount point and file system where the file is located, or the Internet address.
The Repeat Mode
Running lsof with the –r option puts lsof in repeat mode, re-running the command in a loop every few seconds. This mode is useful for monitoring for a process or a connection that might only exist for a short time. The -r command runs forever, so when you are finished you must manually terminate the command.
The +r option also puts lsof in repeat mode – the difference between -r and +r is that +r
automatically terminates lsof when a loop has no new output to print.
When lsof is in repeat mode, it prints new output every t seconds (a loop); the default value
of t is 15 seconds, which you can change by typing an integer value after -r or +r.
The following command tells lsof to display all UDP connections every 10 seconds:
sudo lsof -r 10 -i UDP
Choosing Between IPv4 and IPv6
lsof lists both IPv4 and IPv6 connections by default, but you can choose the kind of connections you want to display. The following command displays IPv4 connections only:
sudo lsof -i4
Therefore, the next command displays all TCP connections of the IPv4 protocol:
sudo lsof -i4 -a -i TCP
An equivalent command to the above is the following command that uses grep:
sudo lsof -i4 | grep TCP
On the other hand, the following command displays IPv6 connections only:
sudo lsof -i6
Therefore, the next command displays all UDP connections of the IPv6 protocol:
sudo lsof -i6 | grep UDP
avahi-dae 669 avahi 13u IPv6 20733 0t0 UDP *:mdns
avahi-dae 669 avahi 15u IPv6 20735 0t0 UDP *:48582
ntpd 848 ntp 16u IPv6 22807 0t0 UDP *:ntp
ntpd 848 ntp 20u IPv6 22818 0t0 UDP localhost:ntp
ntpd 848 ntp 24u IPv6 24916 0t0 UDP [2a01:7e00::f03c:91ff:fe69:1381]:ntp
ntpd 848 ntp 25u IPv6 24918 0t0 UDP [fe80::f03c:91ff:fe69:1381]:ntpLogically ADD All Options
In this section of the guide you learn how to logically ADD the existing options using the -a flag. This provides you enhanced filtering capabilities. Take the following command as an example:
sudo lsof -Pni -u www-data
The above command prints out all network connections (-i), suppressing network number conversion (-n) and the conversion of port numbers to port names (-P). It also prints out all files pertaining to the www-data user, without combining the two options into one logical statement.
The following command combines these two options with the -a logical AND option and finds all open sockets belonging to the www-data user:
lsof -Pni -a -u www-data
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
apache2 6385 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 6385 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 6386 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 6386 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 6387 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 6387 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 24567 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 24567 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 24570 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 24570 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 24585 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 24585 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 25431 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 25431 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 27827 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 27827 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 27828 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 27828 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 27829 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 27829 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)-a option wherever you like as lsof still detects the relevant options.Using Regular Expressions
lsof has support for regular expressions. Regular expressions begin and end with a forward slash (/) character. The ^ character denotes the beginning of a line whereas $ denotes the end of the line. Each dot (.) character represents a single character in the output.
The following lsof command finds all commands that have precisely five characters:
lsof -c /^.....$/
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
netns 18 root cwd DIR 8,0 4096 2 /
netns 18 root rtd DIR 8,0 4096 2 /
netns 18 root txt unknown /proc/18/exe
jfsIO 210 root cwd DIR 8,0 4096 2 /
jfsIO 210 root rtd DIR 8,0 4096 2 /
jfsIO 210 root txt unknown /proc/210/exe
kstrp 461 root cwd DIR 8,0 4096 2 /
kstrp 461 root rtd DIR 8,0 4096 2 /
kstrp 461 root txt unknown /proc/461/exeOutput For Other Programs
Using the -F option, lsof generates output that is suitable for processing by scripts written in programming languages such as awk, perl and python.
The following command displays each field of the lsof output in a separate line:
sudo lsof -n -i4 -a -i TCP:ssh -F
p812
g812
R1
csshd
u0
Lroot
f3
au
l
tIPv4
.
.
.Providing various arguments to the -F option allows you to generate less output. Notice that the process ID and the file descriptor are always printed in the output. As an example, the following command only prints the process ID, which is preceded by the p character, the file descriptor, which is preceded by the f character, and the protocol name of each entry, which is preceded by the P character:
sudo lsof -n -i4 -a -i TCP:ssh -FP
p812
f3
PTCP
p22352
f3
PTCP
p22361
f3
PTCP-F, you should visit the manual page of lsof.Additional Examples
Show All Open TCP Files
Similar to the aforementioned UDP command, the following command displays all open TCP files/connections:
sudo lsof -i TCP
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
sshd 812 root 3u IPv4 23674 0t0 TCP *:ssh (LISTEN)
sshd 812 root 4u IPv6 23686 0t0 TCP *:ssh (LISTEN)
mysqld 1003 mysql 17u IPv4 24217 0t0 TCP localhost:mysql (LISTEN)
master 1245 root 13u IPv4 24480 0t0 TCP *:smtp (LISTEN)
sshd 22352 root 3u IPv4 8613370 0t0 TCP 17-5-7-8.ip.linodeusercontent.com:ssh->ppp-2-8-23-19.home.otenet.gr:60032 (ESTABLISHED)
sshd 22361 mtsouk 3u IPv4 8613370 0t0 TCP 17-5-7-8.ip.linodeusercontent.com:ssh->ppp-2-8-23-19.home.otenet.gr:60032 (ESTABLISHED)
apache2 24565 root 4u IPv6 8626153 0t0 TCP *:http (LISTEN)
apache2 24565 root 6u IPv6 8626157 0t0 TCP *:https (LISTEN)
apache2 24567 www-data 4u IPv6 8626153 0t0 TCP *:http (LISTEN)
apache2 24567 www-data 6u IPv6 8626157 0t0 TCP *:https (LISTEN)
apache2 24568 www-data 4u IPv6 8626153 0t0 TCP *:http (LISTEN)
apache2 24568 www-data 6u IPv6 8626157 0t0 TCP *:https (LISTEN)
apache2 24569 www-data 4u IPv6 8626153 0t0 TCP *:http (LISTEN)
apache2 24569 www-data 6u IPv6 8626157 0t0 TCP *:https (LISTEN)
apache2 24570 www-data 4u IPv6 8626153 0t0 TCP *:http (LISTEN)
apache2 24570 www-data 6u IPv6 8626157 0t0 TCP *:https (LISTEN)
apache2 24571 www-data 4u IPv6 8626153 0t0 TCP *:http (LISTEN)
apache2 24571 www-data 6u IPv6 8626157 0t0 TCP *:https (LISTEN)Listing All ESTABLISHED Connections
Internet Connections
If you process the output of lsof with some traditional UNIX command line tools, like
grep and awk, you can list all active network connections:
sudo lsof -i -n -P | grep ESTABLISHED | awk '{print $1, $9}' | sort -u
sshd 109.74.193.253:22->2.86.23.29:60032lsof -i -n -P command can be also written as lsof -i -nP or alternatively as lsof -nPi – writing it as lsof -inP would generate a syntax error because lsof thinks that np is a parameter to -i.SSH Connections
The following command finds all established SSH connections to the local machine:
sudo lsof | grep sshd | grep ESTABLISHED
253.17-5-7-8.ip.linodeusercontent.com:ssh->ppp-2-86-23-29.home.otenet.gr:60032 (ESTABLISHED)
sshd 22361 mtsouk 3u IPv4 8613370 0t0 TCP 17-5-7-8.ip.linodeusercontent.com:ssh->ppp-2-86-23-29.home.otenet.gr:60032 (ESTABLISHED)The following command produces the same output as the previous command, but does so more quickly because the -i TCP option limits the amount of information lsof prints. That means grep has less data
to process:
sudo lsof -i TCP | grep ssh | grep ESTABLISHED
Alternatively, you can execute the following command to find all established SSH connections:
sudo lsof -nP -iTCP -sTCP:ESTABLISHED | grep SSH
Showing Processes that are Listening to a Particular Port
The following command shows all network connections that listen to port number 22 (ssh) using either UDP or TCP:
sudo lsof -i :22
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
sshd 812 root 3u IPv4 23674 0t0 TCP *:ssh (LISTEN)
sshd 812 root 4u IPv6 23686 0t0 TCP *:ssh (LISTEN)
sshd 22352 root 3u IPv4 8613370 0t0 TCP 17-5-7-8.ip.linodeusercontent.com:ssh->ppp-2-86-23-29.home.otenet.gr:60032 (ESTABLISHED)
sshd 22361 mtsouk 3u IPv4 8613370 0t0 TCP 17-5-7-8.ip.linodeusercontent.com:ssh->ppp-2-86-23-29.home.otenet.gr:60032 (ESTABLISHED)Determine Which Program Listens to a TCP port
One of the most frequent uses of lsof is determining which program listens to a given TCP port. The following command prints TCP processes that are in the LISTEN state by using the -s option to provide a protocol and protocol state:
sudo lsof -nP -i TCP -s TCP:LISTEN
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
sshd 812 root 3u IPv4 23674 0t0 TCP *:22 (LISTEN)
sshd 812 root 4u IPv6 23686 0t0 TCP *:22 (LISTEN)
mysqld 1003 mysql 17u IPv4 24217 0t0 TCP 127.0.0.1:3306 (LISTEN)
master 1245 root 13u IPv4 24480 0t0 TCP *:25 (LISTEN)
apache2 24565 root 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 24565 root 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 24567 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 24567 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 24568 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 24568 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 24569 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 24569 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 24570 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 24570 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 24571 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 24571 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)
apache2 24585 www-data 4u IPv6 8626153 0t0 TCP *:80 (LISTEN)
apache2 24585 www-data 6u IPv6 8626157 0t0 TCP *:443 (LISTEN)Other possible states of a TCP connection are CLOSED, SYN-SENT, SYN-RECEIVED, ESTABLISHED, CLOSE-WAIT, LAST-ACK, FIN-WAIT-1, FIN-WAIT-2, CLOSING, and TIME-WAIT.
Finding Information on a Given Protocol
The next lsof command shows open UDP files that use the NTP (Network Time Protocol) port only:
sudo lsof -i UDP:ntp
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
ntpd 848 ntp 16u IPv6 22807 0t0 UDP *:ntp
ntpd 848 ntp 17u IPv4 22810 0t0 UDP *:ntp
ntpd 848 ntp 18u IPv4 22814 0t0 UDP localhost:ntp
ntpd 848 ntp 19u IPv4 22816 0t0 UDP 17-5-7-8.ip.linodeusercontent.com:ntp
ntpd 848 ntp 20u IPv6 22818 0t0 UDP localhost:ntp
ntpd 848 ntp 24u IPv6 24916 0t0 UDP [2a01:7e00::f03c:91ff:fe69:1381]:ntp
ntpd 848 ntp 25u IPv6 24918 0t0 UDP [fe80::f03c:91ff:fe69:1381]:ntpThe output displays connections that use either IPv4 or IPv6. If you want to display the connections that use IPv4 only, you can run the following command:
sudo lsof -i4 -a -i UDP:ntp
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
ntpd 848 ntp 17u IPv4 22810 0t0 UDP *:ntp
ntpd 848 ntp 18u IPv4 22814 0t0 UDP localhost:ntp
ntpd 848 ntp 19u IPv4 22816 0t0 UDP 17-5-7-8.ip.linodeusercontent.com:ntpDisabling DNS and port Number Resolving
lsof uses the data found in the /etc/services file to map a port number to a service. You can disable this functionality by using the –P option as follows:
lsof -P -i UDP:ntp -a -i4
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
ntpd 848 ntp 17u IPv4 22810 0t0 UDP *:123
ntpd 848 ntp 18u IPv4 22814 0t0 UDP localhost:123
ntpd 848 ntp 19u IPv4 22816 0t0 UDP 17-5-7-8.ip.linodeusercontent.com:123In a similar way, you can disable DNS resolving using the -n option:
lsof -P -i UDP:ntp -a -i4 -n
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
ntpd 848 ntp 17u IPv4 22810 0t0 UDP *:123
ntpd 848 ntp 18u IPv4 22814 0t0 UDP 127.0.0.1:123
ntpd 848 ntp 19u IPv4 22816 0t0 UDP 109.74.193.253:123The -n option can be particularly useful when you have a problem with your DNS servers or when you are interested in the actual IP address.
Find Network Connections From or To an External Host
The following command finds all network connections coming from or going to ppp-2-86-23-29.home.example.com:
sudo lsof -i @ppp-2-86-23-29.home.example.com
sshd 22352 root 3u IPv4 8613370 0t0 TCP 17-5-7-8.ip.linodeusercontent.com:ssh->ppp-2-86-23-29.home.example.com:60032 (ESTABLISHED)
sshd 22361 mtsouk 3u IPv4 8613370 0t0 TCP 17-5-7-8.ip.linodeusercontent.com:ssh->ppp-2-86-23-29.home.example.com:60032 (ESTABLISHED)You can also specify the range of ports that interest you as follows:
sudo lsof -i @ppp-2-86-23-29.home.example.com:200-250
Determine Which Processes are Accessing a Given File
With lsof you can find the processes that are accessing a given file. For example, by running the lsof command on it’s own file you can determine the processes that are accessing it:
sudo lsof `which lsof`
lsof 25079 root txt REG 8,0 163136 5693 /usr/bin/lsof
lsof 25080 root txt REG 8,0 163136 5693 /usr/bin/lsofThere are two lines in the above output because the /usr/bin/lsof file is being accessed twice, by
both which(1) and lsof.
If you are only interested in the process ID of the processes that are accessing a file, you can use the -t option to suppress header lines:
sudo lsof -t `which lsof`
25157
25158A process ID can commonly be used for easily killing a process using the kill(1) command, however this is something that should only be executed with great care.
List Open Files Under a Given Directory
The +D lsof command displays all open files under a given directory, which in this case is /etc, as well as the name of the process that keeps a file or a directory open:
sudo lsof +D /etc
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
avahi-dae 669 avahi cwd DIR 8,0 4096 745751 /etc/avahi
avahi-dae 669 avahi rtd DIR 8,0 4096 745751 /etc/avahiList Files that are Opened by a Specific User
Another option is to locate the files opened by any user, including web and database users.
The following command lists all open files opened by the www-data user:
sudo lsof -u www-data
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
php5-fpm 1066 www-data cwd DIR 8,0 4096 2 /
php5-fpm 1066 www-data rtd DIR 8,0 4096 2 /
...The next variation finds all ESTABLISHED connections owned by the www-data user:
sudo lsof -u www-data | grep -i ESTABLISHED
apache2 24571 www-data 29u IPv6 8675584 0t0 TCP 17-5-7-8.ip.linodeusercontent.com:https->ppp-2-86-23-29.home.otenet.gr:61383 (ESTABLISHED)
apache2 24585 www-data 29u IPv6 8675583 0t0 TCP 17-5-7-8.ip.linodeusercontent.com:https->ppp-2-86-23-29.home.otenet.gr:61381 (ESTABLISHED)
apache2 27827 www-data 29u IPv6 8675582 0t0 TCP 17-5-7-8.ip.linodeusercontent.com:https->ppp-2-86-23-29.home.otenet.gr:61382 (ESTABLISHED)Last, the next command finds all processes except the ones owned by www-data by using the ^ character:
sudo lsof -u ^www-data
COMMAND PID TID USER FD TYPE DEVICE SIZE/OFF NODE NAME
systemd 1 root cwd DIR 8,0 4096 2 /
systemd 1 root rtd DIR 8,0 4096 2 /
systemd 1 root txt REG 8,0 1120992 1097764 /lib/systemd/systemd
...If the user name you are trying to use does not exist, you get an error message similar to the following:
sudo lsof -u doesNotExist
lsof: can't get UID for doesNotExist
lsof 4.89
latest revision: ftp://lsof.itap.purdue.edu/pub/tools/unix/lsof/
latest FAQ: ftp://lsof.itap.purdue.edu/pub/tools/unix/lsof/FAQ
latest man page: ftp://lsof.itap.purdue.edu/pub/tools/unix/lsof/lsof_man
usage: [-?abhKlnNoOPRtUvVX] [+|-c c] [+|-d s] [+D D] [+|-E] [+|-e s] [+|-f[gG]]
[-F [f]] [-g [s]] [-i [i]] [+|-L [l]] [+m [m]] [+|-M] [-o [o]] [-p s]
[+|-r [t]] [-s [p:s]] [-S [t]] [-T [t]] [-u s] [+|-w] [-x [fl]] [--] [names]
Use the ``-h'' option to get more help information.Kill All Processes Owned by a User
The following command kills all of the processes owned by the www-data user:
lsof with the kill(1) command. Do not try to test similar commands on a live server unless you are absolutely certain you will not experience issues. For testing purposes you can use a disposable Docker image or something similar.sudo kill -9 `lsof -t -u www-data`
Find All Network Activity from a Given User
The following command lists all network activity by a user named mtsouk:
lsof -a -u mtsouk -i
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
sshd 22361 mtsouk 3u IPv4 8613370 0t0 TCP 17-5-7-8.ip.linodeusercontent.com:ssh->ppp-2-86-23-29.home.otenet.gr:60032 (ESTABLISHED)On the other hand, the following command lists all network activity from processes not owned by the root or the www-data user:
lsof -a -u ^root -i -u ^www-data
avahi-dae 669 avahi 12u IPv4 20732 0t0 UDP *:mdns
avahi-dae 669 avahi 13u IPv6 20733 0t0 UDP *:mdns
avahi-dae 669 avahi 14u IPv4 20734 0t0 UDP *:54087
avahi-dae 669 avahi 15u IPv6 20735 0t0 UDP *:48582
ntpd 848 ntp 16u IPv6 22807 0t0 UDP *:ntp
ntpd 848 ntp 17u IPv4 22810 0t0 UDP *:ntp
ntpd 848 ntp 18u IPv4 22814 0t0 UDP localhost:ntp
ntpd 848 ntp 19u IPv4 22816 0t0 UDP 17-5-7-8.ip.linodeusercontent.com:ntp
ntpd 848 ntp 20u IPv6 22818 0t0 UDP localhost:ntp
ntpd 848 ntp 24u IPv6 24916 0t0 UDP [2a01:7e00::f03c:91ff:fe69:1381]:ntp
ntpd 848 ntp 25u IPv6 24918 0t0 UDP [fe80::f03c:91ff:fe69:1381]:ntp
mysqld 1003 mysql 17u IPv4 24217 0t0 TCP localhost:mysql (LISTEN)
sshd 22361 mtsouk 3u IPv4 8613370 0t0 TCP 17-5-7-8.ip.linodeusercontent.com:ssh->ppp-2-86-23-29.home.otenet.gr:60032 (ESTABLISHED)Find the Total Number of TCP and UDP Connections
If you process the output of lsof with some traditional UNIX command line tools, like grep and awk,
you can calculate the total number of TCP and UDP connections:
sudo lsof -i | awk '{print $8}' | sort | uniq -c | grep 'TCP\|UDP'
28 TCP
13 UDPThe lsof –i command lists all Internet connections whereas awk extracts the 8th field, which is the value of the NODE column and sort sorts the output. Then, the uniq –c command counts how many times each line exists. Last, the grep –v 'TCP\|UDP' command displays the lines that contain the TCP or the UDP word in them.
Summary
lsof is a powerful diagnostic tool capable of a significant number of ways that you can combine its command line options to troubleshoot various issues administrators can find themselves facing. As this guide has only provided a few examples of how to use this tool, additional options can be combined for various effects that can be specifically suited to your needs.
More Information
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