How to login linux single mode

RHEL 6

Go to the Boot loader Screen, add " single" in the end of kernel
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RHEL 7.9

Go to the Boot loader Screen, change the argument ro to rw init=/sysroot/bin/sh as shown in the screen shot below.

press Ctrl-X or F10 to boot into single user mode 

# mount -o remount,rw /sysroot

# chroot /sysroot/
# reboot -f

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RHEL 8.6

Go to the Boot loader Screen, change the argument

add "rd.break" after quiet

Ctrl + x , boot

# mount -o remount,rw /sysroot

# chroot /sysroot/
# reboot -f

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SLES

Go to the Boot loader Screen, type below command in the boot instruction option :

init=/bin/bash