Why the message "bash fork Cannot allocate memory" occurs during ssh login?

Issue

• The system reboots with the below error message :

-bash: fork: Cannot allocate memory

• Unable to login to the user with the following error on the console.

System error for create: "Cannot allocate memory"

• The system does not respond and gives below error at the login or while running commands.

-bash: fork: Cannot allocate memory

• Kernel logs messages for various system daemons and services as shown below:

Feb 27 16:30:01 uklvapapp577 crond: /usr/sbin/sendmail: Cannot allocate memory
Feb 27 16:30:01 uklvapapp577 crond: /usr/sbin/sendmail: Cannot allocate memory
Feb 27 18:02:05 uklvapapp577 puppet-agent[4848]: Could not run: Cannot allocate memory - fork(2)
Feb 27 18:02:05 uklvapapp577 puppet-agent[4848]: Could not run: Cannot allocate memory - fork(2)
Feb 27 18:29:33 uklvapapp577 systemd: Failed to fork: Cannot allocate memory
Feb 27 18:29:33 uklvapapp577 systemd: Failed to fork: Cannot allocate memory
Feb 27 18:29:33 uklvapapp577 systemd: systemd-tmpfiles-clean.service failed to run 'start' task: Cannot allocate memory
Feb 27 18:29:33 uklvapapp577 systemd: systemd-tmpfiles-clean.service failed to run 'start' task: Cannot allocate memory
Feb 28 04:20:06 uklvapapp577 systemd: Failed to fork: Cannot allocate memory
Feb 28 04:20:06 uklvapapp577 systemd: Failed to fork: Cannot allocate memory
Feb 28 04:20:06 uklvapapp577 systemd: getty@tty1.service failed to run 'start' task: Cannot allocate memory
Feb 28 04:20:06 uklvapapp577 systemd: getty@tty1.service failed to run 'start' task: Cannot allocate memory