Hello Himanshu,
ISIM performs the following command for one of the files /etc/passwd or /etc/shadow, depending if you use or not shadow file:
cat <passwd_or_shadow_file> |grep -e ^<user>:
then it retrieves the following character of the first colon character ":".
If that character is the ASCII-33 "!", then it retuns inactive, else it returns active.
Hope it helps!
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Federico Añino
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