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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 '${LINE}d' ~/.ssh/known_host
2012-01-16 18:00:12
User: lucasrangit
Functions: sed
-5
Remove a line from a file using sed (useful for updating known SSH server keys when they change)

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.

Alternatives

There are 4 alternatives - vote for the best!

Terminal - Alternatives
ssh-keygen -R <thehost>
sed -i '${LINE}d' ~/.ssh/known_host
vi +<lineNumber>d +wq <filename>
2012-01-25 18:28:03
User: detert
Functions: vi
1

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

Know a better way?

If you can do better, submit your command here.

What others think

To remove a line in know_hosts file you can also do

ssh-keygen -R www.example.com
Comment by gilles 188 weeks and 3 days ago

That doesn't actually leave you with an ~/.ssh/know_host file with the line removed anyway.

Comment by DaveQB 186 weeks and 5 days ago

I went for

mv ~/.ssh/known_hosts ~/.ssh/known_hosts.old; sed "${LINE}d" ~/.ssh/known_hosts.old > ~/.ssh/known_hosts

... because not only does ssh-keygen silently fail with the -R option on my (ooooold) system, but sed doesn't know -i either ...

Comment by assarbad 182 weeks and 1 day ago

Your point of view

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