Ubuntu 16.04
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Count attempted Accesses
Count attempted Accesses.
[1] If counts of attempted accesses of a user is over the value, the user account will be locked.
vi /etc/pam.d/common-auth
# deny=N means a user account is locked over N times attempted (root is not applied)

# if also apply to root, add "even_deny_root"

# unlock_time=N means a locked account will be unlocked after N secconds later (if not specified this value, locked account will not be unlocked automatically)

# if specify "even_deny_root", it's also possible to specify locked timed with "root_unlock_time=N"

auth    required        pam_tally2.so deny=5 unlock_time=60
# here are the per-package modules (the "Primary" block)
auth    [success=1 default=ignore]      pam_unix.so nullok_secure
[2] Refer to a count of attempted accesses or unlock a locked account manually like follows.
# show a count of attempted accesses

pam_tally2 -u ubuntu

Login           Failures Latest failure     From
ubuntu              7    04/21/16 19:27:18

# unlock a locked account manually

pam_tally2 -r -u ubuntu