Skip to main content

Lock user account on frequent login failures

Add the following two lines highlighted in blue to the /etc/pam.d/system-auth file as shown below:
auth required
auth required onerr=fail per_user deny=3 reset
auth required
auth sufficient likeauth nullok try_first_pass
auth requisite uid >= 500 quiet
auth required
account required
account required
account sufficient uid < 500 quiet
account required
password requisite try_first_pass retry=3
password sufficient md5 shadow nullok try_first_pass use_authtok
password required
session optional revoke
session required
session [success=1 default=ignore] service in crond quiet use_uid
session required

The first added line counts failed login and failed su attempts for each user. The default location for attempted accesses is recorded in /var/log/faillog.
The second added line specifies to lock accounts automatically after 5 failed login or su attempts (deny=5). The counter will be reset to 0 (reset) on successful entry if deny=n was not exceeded.
But you don't want system or shared accounts to be locked after too many login failures (denial of service attack). To exempt system and shared accounts from the deny=n parameter. The per_user parameter instructs the module NOT to use the deny=n limit for accounts where the maximum number of login failures is set explicitly. For example:
# faillog -u root -m -1
# faillog -u root
Username Failures Maximum Latest
oracle 0 -1 Fri Dec 10 23:57:55 -0600 2005 on unknown
The faillog command with the option "-m -1" has the effect of not placing a limit on the number of failed logins. To instruct the module to activate the deny=n limit for this account again, run:
# faillog -u -m 0
To see failed login attempts, run:
# faillog
To unlock an account after too many login failures, run:
# faillog -u -r
Make sure to test these changes thoroughly on your system using e.g. ssh and su, and make sure root does not get locked!
To lock/unlock accounts manually, you can run one of the following commands:
# passwd -l
# usermod -L
# passwd -u
# usermod -U


Popular posts from this blog

Check remote UDP connectivity from Linux

Hi there, You all know how to check TCP port connectivity from a Linux or UNIX machine to a remote machine using telnet as per th example below $ telnet 25 but we can't adopt TELNET to check UDP connectivity. Linux and most of the UNIXes come with a network layer utility called nc (abbreviation for netcat) which is very useful to check UDP connectivity and to explore a lot with both TCP and UDP. An example is shown below # nc -v -u -z -w 3 123 Connection to 123 port [udp/ntp] succeeded!

The best putty package available

Bored of Black screened Task bar filling putty? Issues with porting Saved sessions from machine to machine? Do you like tabbed SSH sessions? Start using portaputty instead of normal putty and link it with puttycm . Puttycm supports sessions to be saved in its own Database files. You can use the Putty sessions you have saved already right inside putty. You can have any number of databases which allow you to arrange Remote servers in folders and convenient namings. I personally recommend creating Database with puttycm rather than using the sessions saved in putty which doesn't offer any option to create folders and saving sessions under that directory tree. You can even save username/password to get it logged automatically and there is an option to pass commands to be run soon after login. I can't recommend this since some bug was found with these options. Portaputty is a variant of putty which stores all the Configuration data in text files instead of MS Window

#!/usr/bin/env bash ## Ping all machines in a Network PING="$(which ping) -c 1 -W 1" echo "Enter Subnet(eg:192.168.0)" read Subnet echo "Do you want to PING the entire network or a RANGE of IPs ? Enter your choice" echo 1. Ping Entire Network echo 2. Ping a RANGE read choice if [ $choice = 1 ]; then { echo Pinging..... for((i=1;i<255;i++)); do ${PING} ${Subnet}.${i} > /dev/null 2> /dev/null if [ $? -eq 0 ]; then echo -e "${Subnet}.${i} is up" fi done } fi if [ $choice = 2 ]; then { echo Enter the Starting IP of Range read a echo Enter the Last IP of Range read b echo Pinging..... for((i=$a;i<$b;i++)); do ${PING} ${Subnet}.${i} > /dev/null 2> /dev/null if [ $? -eq 0 ]; then echo -e "${Subnet}.${i} is up" fi done } fi exit 0