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2011-03-12 - Confoo 2011 presentation
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Remove a line from a file using sed (useful for updating known SSH server keys when they change)

Terminal - Remove a line from a file using sed (useful for updating known SSH server keys when they change)
sed -i '${LINE}d' ~/.ssh/known_host
2012-01-19 11:22:45
User: richard
Functions: sed
Remove a line from a file using sed (useful for updating known SSH server keys when they change)


There are 5 alternatives - vote for the best!

Terminal - Alternatives
ssh-keygen -R <thehost>
vi +<lineNumber>d +wq <filename>
2012-01-25 18:28:03
User: detert
Functions: vi

For example, to remove line 5 from foo, type: vi +5d +wq foo

perl -p -i -e 's/.*\n//g if $.==2' ~/.ssh/known_hosts
sed '${LINE}d' ~/.ssh/known_host
2012-01-16 18:00:12
User: lucasrangit
Functions: sed

When you SSH to a server who's hostname or IP has changed since the last time a connection was recorded in the known_hosts file a warning will be displayed since this indicated a possible DNS spoofing attack. If this is a known change then this command will remove the previous entry and allow the SSH connection. The SSH client will prompt you as if it was the first time connected to the server.

Replace ${LINE} with the line of the offending key in ~known_hosts. 49 in the sample output.

Know a better way?

If you can do better, submit your command here.

What others think

Probably you want '~/.ssh/known_hosts' (mind the final 's').

Comment by funollet 166 weeks and 2 days ago

This command isn't portable across unices, has a typo, and requires you to know the line before running this command. Using ssh-keygen(1) is the preferred, portable way.

Comment by atoponce 166 weeks and 2 days ago

Portable is relative. I have an old Redhat system here that doesn't even know the -i switch to sed ;)

Comment by assarbad 160 weeks and 3 days ago

Your point of view

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