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linux:sysadmin [2016/07/12 21:19]
mstraub [Network Configuration]
linux:sysadmin [2020/08/20 11:59] (current)
mstraub [Check Open Ports & Connections]
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 # │   ​│ ​  ​│ ​  ​│ ​  ​| ​  ​│ ​   └ command # │   ​│ ​  ​│ ​  ​│ ​  ​| ​  ​│ ​   └ command
 # │   ​│ ​  ​│ ​  ​│ ​  ​| ​  ​└───── user executing the command # │   ​│ ​  ​│ ​  ​│ ​  ​| ​  ​└───── user executing the command
-# │   ​│ ​  ​│ ​  ​│ ​  ​└───────── day of week (0 - 7) (0 to 7 are Sunday to Sunday, or use names) +# │   ​│ ​  ​│ ​  ​│ ​  ​└───────── day of week (0 - 7) (0 to 7 are Sunday to Sunday, or use names such as MON-FRI
-# │   ​│ ​  ​│ ​  ​└───────────── month (1 - 12)+# │   ​│ ​  ​│ ​  ​└───────────── month (1 - 12) (or names such as JAN-DEC)
 # │   ​│ ​  ​└───────────────── day of month (1 - 31) # │   ​│ ​  ​└───────────────── day of month (1 - 31)
 # │   ​└───────────────────── hour (0 - 23) # │   ​└───────────────────── hour (0 - 23)
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 </​code>​ </​code>​
  
 +[[https://​crontab.guru|nifty online editor]]
 ==== More crontab ==== ==== More crontab ====
 Also possible, but not encouraged in order to not put cron jobs into too many different places and overcomplicate administration,​ are the following options: Also possible, but not encouraged in order to not put cron jobs into too many different places and overcomplicate administration,​ are the following options:
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 <code bash> <code bash>
 netstat -a           # print open & listening internet connections and Unix domain sockets netstat -a           # print open & listening internet connections and Unix domain sockets
-netstat -a -t        # print only tcp connections (-u for udp) +netstat -a -t -p     # print only tcp connections (-u for udp) and the associated pid
 netstat -s           # print statistics about e.g. nr of received packets netstat -s           # print statistics about e.g. nr of received packets
 netstat -r           # print the kernel routing table netstat -r           # print the kernel routing table
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 nmap localhost ​      # print open ports on current machine (only a selection of common ports) nmap localhost ​      # print open ports on current machine (only a selection of common ports)
 nmap -p 1-9999 host  # print open ports on a host (with a defined port range) nmap -p 1-9999 host  # print open ports on a host (with a defined port range)
 +nmap -Pn -p 1-9999 host  # as above, but skip host discovery (helpful if above probe fails) ​
 nmap -A -T4 host     # print open ports with enabled version detection (-A) and don't wait too long (-T4) nmap -A -T4 host     # print open ports with enabled version detection (-A) and don't wait too long (-T4)
 </​code>​ </​code>​
linux/sysadmin.1468351183.txt.gz · Last modified: 2016/07/12 21:19 by mstraub