POSTS

Changing SSH Port in One Line

Sometimes you just want to change the port which SSH listens on

Solution

sed -i.bak -Ee 's/^#?Port\s+[0-9]*$/Port 2222/g;' /etc/ssh/sshd_config

What’s Happening?

First off for those who have never heard of or used sed it is a very powerful tool. sed is a stream editor for filtering and transforming text used to perform basic transformations on an input stream (a file or input from a pipeline). This means you can essentially transform text per line once a set of conditions have been met. Observe: * -i.bak This will set sed to edit the file inplace and makes backup since we supplied .bak. Removing the .bak will not create a backup * -E This will enable extended regular expressions like + * -e The expression we wish to use, I’ll explain this below

Now sed lets break down the expressions s/^#?Port\s+[0-9]*$/Port 2222/g;: * s - This stands for substitution and will replace matches defined in the first argument for the second * / - Denotes the stand of the first parameter of the find. * ^#?Port\s+[0-9]*$ - A regular expression we use to match a number of ways the Port parameter can be represented. These include active(Port 1) and commented out(#Port 12) * / - Denotes the start of the second parameter to be substituted in * Port 2222 - Our port we wish to bind on * / - End of the second parameter * g - Sets the substitution to affect globally encase we have multiple instances of Port defined.

Finally we specify the file we wish to edit which is /etc/ssh/sshd_config

Footnote

A more bullet proof guide can be found here