Quick summary of useful program in Linux for sysadmin purposes. To get a full description of each one have a look at their man pages, by doing man command

Powerful file finder on the whole system, run after sudo updatedb. Need to be explicitly installed

Syntax:
plocate test.txt

Output:

/home/admin/test.txt

Print a folder structure. Need to be explicitly installed

Syntax:
tree /home/admin/TreeFolder/

Output:

/home/admin/TreeFolder/
├── SubTreeFolder
│   └── SubTreeFile
└── TreeFile

Follow a pathname until a terminal point is found. Need to be explicitly installed

Syntax:
namei /home/admin/

Output:

f: /home/admin/
 d /
 d home
 d admin

Print last n rows of a file. Useful to have it printing live updates to a logfile and redirecting the output to analyze it later. The following example is for captirunig a SIP request to analyze it with Wireshark.

Syntax:
tail -f /etc/servicepattern/sipprocessor.log > test.log

Output: The file itself. In this example download the file and open it in Wireshark (or manually).

Let you see running program listening on ports. Many more options in the manpage, use it with grep to look for a specific port.

Syntax:
netstat -tulpn

Output:

Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:5355            0.0.0.0:*               LISTEN      345/systemd-resolve 
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      699/exim4           
tcp        0      0 0.0.0.0:443             0.0.0.0:*               LISTEN      3247/nginx: master  
tcp        0      0 127.0.0.53:53           0.0.0.0:*               LISTEN      345/systemd-resolve 
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      3247/nginx: master  
tcp        0      0 127.0.0.54:53           0.0.0.0:*               LISTEN      345/systemd-resolve 
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      62083/sshd: /usr/sb 
tcp6       0      0 :::5355                 :::*                    LISTEN      345/systemd-resolve 
tcp6       0      0 :::5000                 :::*                    LISTEN      3905/node /home/adm 
tcp6       0      0 ::1:25                  :::*                    LISTEN      699/exim4           
tcp6       0      0 :::80                   :::*                    LISTEN      3247/nginx: master  
tcp6       0      0 :::22                   :::*                    LISTEN      62083/sshd: /usr/sb 
udp        0      0 127.0.0.54:53           0.0.0.0:*                           345/systemd-resolve 

Syntax:
netstat -tulpn | grep 5000

Output:

tcp6       0      0 :::5000                 :::*                    LISTEN      3905/node /home/adm

— Lorenzo Cesana 2026/04/16 09:03