Showing posts with label telnet. Show all posts
Showing posts with label telnet. Show all posts

Friday, June 23, 2017

how to check list of opened and closed port in linux ?

There are different commands on both Linux and UNIX server to see what TCP/UDP ports are listening or open on your server. You can use netstat command, which prints network connections, routing tables, interface statistics, masquerade connections, and multicast memberships, etc.

Method 1:
netstat command to find open ports

Syntax :

netstat --listen

Or

netstat -l

Example:

ravi@linuxforfreshers.com>>sudo netstat --listen
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State     
tcp        0      0 *:1234                  *:*                     LISTEN    
tcp        0      0 *:8084                  *:*                     LISTEN    
tcp        0      0 192.168.122.1:domain    *:*                     LISTEN    
tcp        0      0 *:ssh                   *:*                     LISTEN    
tcp        0      0 *:ipp                   *:*                     LISTEN    
tcp        0      0 *:microsoft-ds          *:*                     LISTEN    
tcp        0      0 *:7070                  *:*                     LISTEN    
tcp        0      0 localhost:mysql         *:*                     LISTEN    
tcp        0      0 *:netbios-ssn           *:*                     LISTEN       
tcp6       0      0 [::]:ssh                [::]:*                  LISTEN    
tcp6       0      0 [::]:ipp                [::]:*                  LISTEN    
tcp6       0      0 [::]:microsoft-ds       [::]:*                  LISTEN    
tcp6       0      0 [::]:netbios-ssn        [::]:*                  LISTEN    
udp        0      0 *:39505                 *:*                               
udp        0      0 *:ipp                   *:*                               
udp        0      0 *:mdns                  *:*                               
udp        0      0 *:mdns                  *:*                               

Active UNIX domain sockets (only servers)
Proto RefCnt Flags       Type       State         I-Node   Path
unix  2      [ ACC ]     STREAM     LISTENING     12950    /var/run/acpid.socket
unix  2      [ ACC ]     STREAM     LISTENING     18259042 @atpl-com.canonical.Unity.Scope.rhythmbox.T516689809663571
unix  2      [ ACC ]     STREAM     LISTENING     19096    /run/user/1000/keyring-n7CcyZ/control
unix  2      [ ACC ]     STREAM     LISTENING     22589    @/tmp/.ICE-unix/3779
unix  2      [ ACC ]     STREAM     LISTENING     21540    @/tmp/dbus-u6IauIGH5I

To display open ports and established TCP connections, enter:

netstat -vatn

Example:

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State     
tcp        0      0 0.0.0.0:1234            0.0.0.0:*               LISTEN    
tcp        0      0 0.0.0.0:8084            0.0.0.0:*               LISTEN    
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:631             0.0.0.0:*               LISTEN    
tcp        0      0 0.0.0.0:445             0.0.0.0:*               LISTEN    
tcp        0      0 0.0.0.0:7070            0.0.0.0:*               LISTEN    

To display only open UDP ports try the following command:

netstat -vaun

Example:

ravi@linuxforfreshers.com>>sudo netstat -vaun
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State     
udp        0      0 0.0.0.0:39505           0.0.0.0:*                         
udp        0      0 0.0.0.0:631             0.0.0.0:*   

Using netstat -lntu

Where
     -l = only services which are listening on some port
     -n = show port number, don't try to resolve the service name
     -t = tcp ports
     -u = udp ports
     -p = name of the program          


Method 2:

Using lsof Command

To display the list of open ports, enter:
# lsof -i
To display all open files, use:
# lsof

To display all open IPv4 network files in use by the process whose PID is 10050, use:
# lsof -i 4 -a -p 10050

Another example:
# lsof -iTCP -sTCP:LISTEN

Method 3:

Using telnet

Quickest way to test if a TCP port is open (including any hardware firewalls you may have), is to type, from a remote computer (e.g. your desktop):

Syntax:

telnet hostip port_number

Example 1:

ravi@linuxforfreshers.com>>telnet 192.168.101.156 22
Trying 192.168.101.156...
Connected to 192.168.101.156
Escape character is '^]'.

Example 2:

ravi@linuxforfreshers.com>>telnet localhost 22
Trying 127.0.0.1...
Connected to localhost.

Method 3:

Using ss command

Syntax:
ss -lntu
Example:

ravi@linuxforfreshers.com>>ss -lntu
Netid State      Recv-Q Send-Q                                                                                     Local Address:Port                                                                                       Peer Address:Port
tcp   UNCONN     0      0                                                                                                      *:39505                                                                                                 *:*    
tcp   UNCONN     0      0                                                                                                      *:631                                                                                                   *:*    
tcp   UNCONN     0      0                                                                                                      *:5353                                                                                                  *:*