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HowTo: Configure Linux To Track and Log

Failed Login Attempt Records

Under Linux operating system you can use the faillog command to display faillog records or toset login failure limits. faillog command displays the contents of the failure log from

/var/log/faillog database file. It also can be used for maintains failure counters and limits. If you

run faillog command without arguments, it will display only list of user faillog records who haveever had a login failure.

PAM Settings

I found that under RHEL / CentOS Linux 5.x, you need to modify /etc/pam.d/system-auth file.

You need to configure a PAM module pam_tally.so. Otherwise faillog command will never

display failed login attempts.

PAM Configuration To Recored Failed Login Attempts

pam_tally.so module maintains a count of attempted accesses, can reset count on success, can

deny access if too many attempts fail. Edit /etc/pam.d/system-auth file, enter:# vi /etc/pam.d/system-authModify as follows:auth required pam_tally.so no_magic_rootaccount required pam_tally.so deny=3 no_magic_root lock_time=180Where,

deny=3 : Deny access if tally for this user exceeds 3 times. lock_time=180 : Always deny for 180 seconds after failed attempt. There is also

unlock_time=n option. It allow access after n seconds after failed attempt. If this option

is used the user will be locked out for the specified amount of time after he exceeded his

maximum allowed attempts. Otherwise the account is locked until the lock is removed bya manual intervention of the system administrator.

magic_root : If the module is invoked by a user with uid=0 the counter is notincremented. The sys-admin should use this for user launched services, like su, otherwise

this argument should be omitted.

no_magic_root : Avoid root account locking, if the module is invoked by a user withuid=0

Save and close the file.

How Do I Display All Failed Login Attempts For a User

Called vivek?

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Type the command as follows:# faillog -u vivek

Login Failures Maximum Latest Onvivek 3 0 12/19/07 14:12:53 -0600 64.11.xx.yy

Taks: Show Faillog Records For All Users

Type the following command with the -a option:# faillog -a

Task: Lock Account

To lock user account to 180 seconds after failed login, enter:# faillog -l 180 -u vivek# faillog -l 180

Task: Set Maximum Number of Login Failures

The -m option is allows you to set maximum number of login failures after the account is

disabled to specific number called MAX. Selecting MAX value of 0 has the effect of not placinga limit on the number of failed logins. The maximum failure count should always be 0 for root to

prevent a denial of services attack against the system:# faillog -M MAX -u username# faillog -M 10 -u vivek

How do I Reset The Counters Of Login Failures?

The -r option can reset the counters of login failures or one record if used with the -u

USERNAME option:# faillog -rTo reset counter for user vivek, enter:# faillog -r -u vivek

On large Linux login server, such as University or government research facility, one might find it

useful to clear all counts every midnight or week from acron job.# crontab -eReset failed login recover every week:@weekly /usr/bin/faillog -rSave and close the file.

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