I'd like to see if somebody has been trying to log-in by brute-force into my Ubuntu 12.04 server over SSH. How can I see if such activities have been taking place?


3 Answers 3


All login attempts are logged to /var/log/auth.log.

1. Filter for brute-force interactive SSH logins

Open a terminal, and type the below; if it's longer than 1 page you will be able to scroll up and down; type q to exit:

grep sshd.\*Failed /var/log/auth.log | less
  • Here's a real example from one of my VPSs:

    Aug 18 11:00:57 izxvps sshd[5657]: Failed password for root from port 38980 ssh2
    Aug 18 23:08:26 izxvps sshd[5768]: Failed password for root from port 38156 ssh2
    Aug 18 23:08:30 izxvps sshd[5770]: Failed password for nobody from port 38556 ssh2
    Aug 18 23:08:34 izxvps sshd[5772]: Failed password for invalid user asterisk from port 38864 ssh2
    Aug 18 23:08:38 izxvps sshd[5774]: Failed password for invalid user sjobeck from port 39157 ssh2
    Aug 18 23:08:42 izxvps sshd[5776]: Failed password for root from port 39467 ssh2

2. Look for failed connections (i.e. no login attempted, could be a port scanner, etc.):

Use this command:

grep sshd.*Did /var/log/auth.log | less
  • Example:

    Aug  5 22:19:10 izxvps sshd[7748]: Did not receive identification string from
    Aug 10 19:39:49 izxvps sshd[1919]: Did not receive identification string from
    Aug 13 23:08:04 izxvps sshd[3562]: Did not receive identification string from
    Aug 17 15:49:07 izxvps sshd[5350]: Did not receive identification string from
    Aug 19 06:28:43 izxvps sshd[5838]: Did not receive identification string from

How to reduce failed/brute-force login attempts

  • Try switching your SSH to a non-standard port from the default 22
  • Or install an auto-ban script such as fail2banInstall fail2ban.
  • 6
    How much security do you get in switching the SSH port (can't they just scan you anyway as you mention) and is it worth that minor usability hit for legitimate users?
    – Nick T
    Commented Aug 2, 2013 at 0:48
  • 12
    @NickT it turns out to be enough to significantly reduce login attempts. Where I'd get thousands of attempts in a week/day, so far I haven't had any for the last month, simply by switching the port.
    – AntoineG
    Commented Mar 10, 2014 at 14:30
  • 2
    I think disallow login with password may helps too.
    – Luc M
    Commented Dec 1, 2015 at 20:16
  • 2
    i know this is ubuntu, just wanted to mention that on some systems like centos the file path is /var/log/secure Commented Jan 12, 2016 at 3:40
  • Some systems access the log with systemctl -eu sshd
    – alecdwm
    Commented Apr 9, 2016 at 14:14

I would argue that monitoring logs is a weak solution especially if you have a weak password on an account. Brute attempts often try at least hundreds of keys per minute. Even if you have a cron job set to email you of brute attempts, it could be hours before you get to your server.

If you have a public-facing SSH server, you need a solution that kicks in long before you can be hacked.

I would strongly recommend fail2ban. Their wiki says what it does better than I can.

Fail2ban scans log files (e.g. /var/log/apache/error_log) and bans IPs that show the malicious signs -- too many password failures, seeking for exploits, etc. Generally Fail2Ban then used to update firewall rules to reject the IP addresses for a specified amount of time, although any arbitrary other action (e.g. sending an email, or ejecting CD-ROM tray) could also be configured. Out of the box Fail2Ban comes with filters for various services (apache, curier, ssh, etc).

Getting protection from it is as simple as sudo apt-get install fail2ban.

By default as soon as somebody has three failed attempts, their IP gets a five minute ban. That sort of delay essentially halts a SSH brute force attempt but it's not going to ruin your day if you forget your password (but you should be using keys anyway!)

  • 8
    Why's it called fail to ban?
    – Pacerier
    Commented Apr 22, 2015 at 3:38
  • 13
    @Pacerier Well with some analogy, login failure leads to(2) a ban.
    – Sebi
    Commented May 9, 2015 at 13:06
  • 3
    Bwahaha you made my day @Pacerier I never thought of it as a literal "failure to ban". Commented Jul 18, 2016 at 5:18
  • 1
    I think this should be edited to remove "especially" from the first sentence. It's only a problem if you have a weak password. Strong passwords cannot be brute forced under any circumstance, and the only reason to prevent people from trying is to reduce server load. Commented Feb 14, 2017 at 1:44
  • Absolutely agree. Anyway it will be ok prevent a highly server load. I have seen attempts at by miliseconds rates Commented Jun 27, 2019 at 16:16

Short Answer: To keep track of the failed attempts, you should just view the log file /var/log/auth.log without using any pattern matching commands because those patterns are not exhaustive. Then, to mitigate it, you could use tools like fail2ban.

Long Answer: There are many ways for invalid logins to happen. For example, an attacker might try some default usernames and passwords like the default "kali" username and "kali" password on Kali Linux. (It is a technique German hackers used extensively during the Cold War era. Read The Cuckoo's Egg if you are interested.)

Say if you remove the "kali" user, the grep commands above won't catch this:

Nov 25 07:11:32 Everything20170707 sshd[27216]: input_userauth_request: invalid user kali [preauth]

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