Restrict maximum simultaneous logins on Linux

Want to restrict simultaneous number of logins attempt on Linux machine? Here is the quick way of doing it.

1. Edit the file /etc/security/limits.conf to make the below changes:

#cat /etc/security/limits.conf

# /etc/security/limits.conf
#
#Each line describes a limit for a user in the form:
#
#
#
#Where:
# can be:
# – an user name
# – a group name, with @group syntax
# – the wildcard *, for default entry
# – the wildcard %, can be also used with %group syntax,
# for maxlogin limit
# – NOTE: group and wildcard limits are not applied to root.
# To apply a limit to the root user, must be
# the literal username root.
#
# can have the two values:
# – “soft” for enforcing the soft limits
# – “hard” for enforcing hard limits
#
# can be one of the following:
# – core – limits the core file size (KB)
# – data – max data size (KB)
# – fsize – maximum filesize (KB)
# – memlock – max locked-in-memory address space (KB)
# – nofile – max number of open files
# – rss – max resident set size (KB)
# – stack – max stack size (KB)
# – cpu – max CPU time (MIN)
# – nproc – max number of processes
# – as – address space limit (KB)
# – maxlogins – max number of logins for this user
# – maxsyslogins – max number of logins on the system
# – priority – the priority to run user process with
# – locks – max number of file locks the user can hold
# – sigpending – max number of pending signals
# – msgqueue – max memory used by POSIX message queues (bytes)
# – nice – max nice priority allowed to raise to values: [-20, 19]
# – rtprio – max realtime priority
# – chroot – change root to directory (Debian-specific)
#
#
#

#* soft core 0
#root hard core 100000
#* hard rss 10000
#@student hard nproc 20
#@faculty soft nproc 20
#@faculty hard nproc 50
#ftp hard nproc 0

Say I want to restrict root user to maximum 3 login sessions.

root soft maxlogins 3

Save this file.
That’s it.