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My /var/log/btmp file is 1.3 GB in size. I've read that the file is "Used to store information about failed login".

What does this mean for my server? And can i delete this file?

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3 Answers

up vote 18 down vote accepted

This means people are trying to brute-force your passwords (common on any public-facing server).

It shouldn't cause any harm to clear out this file.

One way to reduce this is to change the port for SSH from 22 to something arbitrary. For some additional security, DenyHosts can block login attempts after a certain number of failures. I'd highly recommend installing and configuring it.

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You could also examine the file with the lastb command and determine the IP number and maybe block the IP number or network from further accessing your machine. This will also provide information as to the account being hacked. Most likely it will be root but you never know

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fail2ban can also be a great help for machines that must keep internet facing, port 22 SSH. It can be configured to use hosts.allow or iptables with flexible thresholds.

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