Ssh logging in linux

How to Enable SSH Log and List Failed Login in Linux

As we know SSH protocol provide remote login facility and hence it is important to maintain the login logs. System admin can achieve this by configuring in syslogd services.

In Linux, syslogd is the unix logging service that maintains the logs that are sent by the programs to the syslog daemon, syslogd forwards them to another destination such as a console or a file. Destination is specified in the syslog configuration file /etc/syslog.conf.

In this tutorial we will learn how to enable ssh log and check Linux command to list failed ssh login attempts.

Enable syslog Logging

Lets first check config file whether ssh logging enabled or not, use the following command:

By default, ssh logging is enabled, if not enable then enable SSH logging we need to configure the syslog.conf by adding in /etc/syslog.conf file.

When SSH server runs, it will produce the log messages in sshd.log to describe what is going on. These log messages will help the system administrator to track the system details such as who logged in and logged out and to troubleshoot the problem.

The /etc/ssh/sshd_config file is a system-wide configuration file for open SSH service which allows you to set options that modify the operation of the daemon. This configuration file contains keyword-value pairs and one per line with keywords being case sensitive.

SyslogFacility AUTH and AUTHPRIV

Messages received by syslogd are processed according to their facility which indicates a the origin of the message. Standard SyslogFacility includes KERN (Messages from the OS Kernel), DAEMON (Messages from the Service or Daemon), USER (Messages from the user processes), MAIL (Messages from the email System) and others.

By default, the facility for SSH server messages is AUTHPRIV. This choice may be changed with the SSH keyword SyslogFacility which determines the syslog facility code for logging SSH Messages. Other possible values of SyslogFacility are DAEMON, USER, AUTH, AUTHPRIV, LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6 and LOCAL7. The default is AUTHPRIV.

The option SyslogFacility specifies the facility code used when logging messages from sshd. The facility specifies the subsystem that produced the message—in our case, AUTH.

Normally, all authentication related messages are logged with the AUTHPRIV (or AUTH) facility [intended to be secure and never seen by unwanted eyes], while normal operational messages are logged with the DAEMON facility.

Enable Auth in sshd_config file

LogLevel

It gives the verbosity level that is used when logging messages from sshd. The possible other values are QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3. The default is INFO. DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify higher levels of debugging the out-put.

If you want to record more information such as failed login attempts, then you should increase the logging level to VERBOSE.

Make sure to uncomment the below lines to enable loglevel.

Now you need to Restart ssh service

To enable the service of SSH, use the service sshd start command.

You can use watch command to see live ssh log file updates.

Check failed ssh login

You can use any of the below commands to check failed ssh login session on Centos and Ubuntu.

On Centos and Redhat

On Centos 7 and newer Linux distros using systemd

If you had auditd package installed, then you can use aureport tool to get authentication report. To get a report for all the failed attempts made:

Conclusion

There are mainly 3 different log managers available to Linux to collect and store logs. The default is syslog, other two are rsyslog and Syslog-ng.

Newer Linux distros use systemd’s logging service, which uses Journalctl for querying and displaying logs from journald.

I hope you enjoyed reading this tutorial on ssh logging and please leave your thoughts on this tutorial in the below comment section.

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How to Find All Failed SSH login Attempts in Linux

Each attempt to login to SSH server is tracked and recorded into a log file by the rsyslog daemon in Linux. The most basic mechanism to list all failed SSH logins attempts in Linux is a combination of displaying and filtering the log files with the help of cat command or grep command.

In order to display a list of the failed SSH logins in Linux, issue some of the commands presented in this guide. Make sure that these commands are executed with root privileges.

The most simple command to list all failed SSH logins is the one shown below.

List All Failed SSH Login Attempts

The same result can also be achieved by issuing the cat command.

In order to display extra information about the failed SSH logins, issue the command as shown in the below example.

Find Failed SSH Logins

In CentOS or RHEL, the failed SSH sessions are recorded in /var/log/secure file. Issue the above command against this log file to identify failed SSH logins.

Find Failed SSH Logins in CentOS

A slightly modified version of the above command to display failed SSH logins in CentOS or RHEL is as follows.

Find SSH Authentication Failure Logins

To display a list of all IP addresses that tried and failed to log in to the SSH server alongside the number of failed attempts of each IP address, issue the below command.

Find IP Addresses of SSH Failed Logins

On newer Linux distributions you can query the runtime log file maintained by Systemd daemon via journalctl command. In order to display all failed SSH login attempts you should pipe the result via grep filter, as illustrated in the below command examples.

Find Real Time Failed SSH Logins

In CentOS or RHEL, replace the SSH daemon unit with sshd.service, as shown in the below command examples.

After you’ve identified the IP addresses that frequently hit your SSH server in order to log in to the system with suspicious user accounts or invalid user accounts, you should update your system firewall rules to block the failed SSH attempts IP addresses or use a specialized software, such as fail2ban to manage these attacks.

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Where does Ubuntu 14.04 log SSH access attempts? [duplicate]

Trying to find out why fail2ban is not working.

Where does Ubuntu 14.04 log SSH access attempts?

2 Answers 2

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

Search for brute-force SSH logins

Run this command:

Search for failed connections

Run this command:

UPDATE:

You should try restarting the syslog daemon to see if it starts to log to the correct file.

Once you have messages going to the auth.log it should start working.

The default log settings for ssh are «INFO».

If you want to have it include login attempts in the log file, you’ll need to edit the /etc/ssh/sshd_config file and change the «LogLevel» from INFO to VERBOSE .

After that, restart the sshd daemon with

After that, the ssh login attempts will be logged into the /var/log/auth.log file.

Not the answer you’re looking for? Browse other questions tagged 14.04 ssh log or ask your own question.

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How to log ssh client connection/command?

I would like to know how i could log SSH command lines a user is using on a server. For exemple, if the user Alex on my server is doing the following set of commands :

I would like to log the ssh commands used on the server in a file which looks like :

I don’t care what he did during his ssh session, i just want to know WHEN and TO WHERE he made a connection to another server.

The user is not using bash and i would like to avoid manipulating .bash_history anyway as the user can modify it.

Any clue on this ?

edit : to be more specific :

a user connects to a server A and then connects from the server A to server B. I want to track down to which server he connects through ssh from server A.

3 Answers 3

You could do it in three different ways as i see it — There are most likely many other ways to do it as well! The best method would be to attach a audit tool to the kernels sysexec calls so it would be untraceable by the user etc. The two other ways would simply be to modify the shell environment to log it.

Instead of me (grabbing the code/answers from google) showing you how to do it. I will give you links to sites that have explained this detailed already. I hope it’s exactly what you need.

Btw, the easiest way is by far just to include something in your main bashrc/profile to affect all users.

Anyway’s, here are links to bashrc solutions.

The other way (kernel level) would be to look into to tools audit or acct. There are many sites out there who tell you how to setup logging of commands via kernel sysexec calls.

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Logging SSH access attempts

I’ve configured an ubuntu server with openssh in order to connect to it and execute commands from a remote system like a phone or a laptop. The problem is. I’m probably not the only one.

Is there a way to know all the login attempts that have been made to the server?

7 Answers 7

On Ubuntu servers, you can find who logged in when (and from where) in the file /var/log/auth.log . There, you find entries like:

On Red Hat based distros such as Fedora/CentOS/RHEL you can check for the users logged in inside the file /var/log/secure .

Note that the default configuration on Ubuntu is to NOT log ssh logins to the /var/log/auth file. This is the INFO logging level.

If you want to have it include login attempts in the log file, you’ll need to edit the /etc/ssh/sshd_config file (as root or with sudo) and change the LogLevel from INFO to VERBOSE .

After that, restart the sshd daemon with

After that, the ssh login attempts will be logged into the /var/log/auth.log file.

On Ubuntu you can log in via SSH and use the Linux tail command to display the last x number of lines of your /var/log/auth.log file. When you’re logged in via SSH use the following command to view 100 last lines of your SSH log:

or even cleaner

My recommendation is to use auditd. This is logging using the linux kernel’s audit subsystem and in my opinion the proper way to do it if you are serious. And given the nature of the question you should be using PAM as well. At the default level of just having auditd and PAM installed, you should automatically be getting all successful and unsuccessful SSH attempts logged in your audit.log file. So you really don’t have to configure anything, just have auditd and PAM installed. I know this first hand for SLES. And would bet RHEL and any other enterprise version of linux would operate similarly.

within the raw audit log generated by auditd you can use either use something like aureport to filter it which is described in the auditd man pages, write your own text parser, or just use VI and search for keywords.

here is an except of my /var/log/audit/audit.log file with me ssh’ing into my linux server.

• from the above, my server name is shark.
• many lines like this are in audit.log, I want this one based on exe=»/usr/sbin/sshd»
• the uid of the account being ssh’d into is the value of auid, which is 23456 for this example
• the name of the user account associated with auid is specified by acct=»ron»
• most times the audit system will record the dns hostname of the system trying to connect, but it always has it’s ip address
• the date of the entry which is in epoch time, so you’ll have to convert that via something like date —date @1480622612.317 which results in Thu Dec 1 15:03:32 EST 2016 and is when I ssh’d into my server.

When res=failed is when you want to investigate those ip addresses and hostnames to see what systems were trying to connect, under what attempted user name. And obviously the successful ssh attempts to understand what’s happening on your system — for example your coworker bob who sits at same desk everyday with hostname=bobscomputer and ip address=192.168.5.5; if you see a successful ssh attempt at 2am yesterday under his username from ip address 10.10.5.6 for example then it might be in your best interest to talk to bob to investigate. Possible hack attempt by someone else? And shortly after are there su attempts to root in audit log from bob’s account?

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