02-20-2016
Login cancellation question
Purely out of curiosity, but what would happen in all accounts were locked out from being able to be logged in to?? The root account, on most unix-based systems, is locked by default. What if all other login-enabled accounts were changed to be login-disabled?? If such a thing were possible, would there be a possibility of using some way to gain control over the system without being able to login?? Or would the system and its contents be inaccessible?? This is pure curiosity. Obviously, I would never do this if it were possible.
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usermod(8) System Manager's Manual usermod(8)
NAME
usermod - modify a user account
SYNOPSIS
usermod [-D binddn] [-P path] [-g gid [-o]] [-p password]
[--service service] [--help] [--usage] [-v] account
DESCRIPTION
usermod modifies an user account using the values specified on the command line.
OPTIONS
-A, --add-to-group group,...
With this option a list of groups can be specified, which the user should become a member of. Each group is separated from the next
one only by a comma, without whitespace.
-c, --comment comment
This option specifies the new users finger information. It is normally modified using the chfn(1) utility.
-d, --home homedir
This option specifies the new home directory of the user.
-e, --expire expire
With this option the date when the account will be expired can be changed. expiredate has to be specified as number of days since
January 1st, 1970. The date may also be expressed in the format YYYY-MM-DD.
-f, --inactive inactive
This option is used to set the number of days of inactivity after a password has expired before the account is locked. A user whose
account is locked must contact the system administrator before being able to use the account again. A value of -1 disables this
feature.
-G, --groups group,...
With this option a list of supplementary groups can be specified, which the user should become a member of. Each group is separated
from the next one only by a comma, without whitespace. The user is removed from all other groups not specified.
-g, --gid gid
The group name or number of the user's new primary group. The group name must exist and a group number must refer to an already
existing group.
-l, --login name
Specify the new account name for the user. The account name must begin with an alphabetic character and the rest of the string
should be from the POSIX portable character class. Nothing else is changed.
-m, --move_home
Move the user's home directory to the new directory specified with the -d option. If the old directory does not exist, nothing is
done. If the new directory already exists, the program aborts with an error.
-o, --non-unique
Allow duplicate (non-unique) User IDs.
-p, --password password
Encrypted password as returned by crypt(3) as the new password.
-R, --remove-from-group group,...
With this option a list of groups can be specified, from which the user should be removed. Each group is separated from the next one
only by a comma, without whitespace.
-s, --shell shell
Specify user's new login shell. The value of shell must be a valid executable file. It is normally modified using the chsh(1) util-
ity.
-u, --uid uid
Change the userid to be the given number. This value must be positive and unique (unless the -o option is used). Any file with the
old UID of the user and which is located in the directory tree rooted at the user's home directory will be changed to be owned by
the new UID automatically.
-D, --binddn binddn
Use the Distinguished Name binddn to bind to the LDAP directory. The user will be prompted for a password for simple authentica-
tion.
-L, --lock
A system administrator can lock the account of the specified user.
-U, --unlock
A system administrator can unlock the specified account, if the account is not passwordless afterwards (it will not unlock an
account that has only "!" as a password).
-P, --path path
The passwd and shadow files are located below the specified directory path. usermod will use this files, not /etc/passwd and
/etc/shadow.
--service service
Modify the account from a special directory. The default is files, but ldap is also valid.
--help Print a list of valid options with a short description.
--usage
Print a short list of valid options.
-v, --version
Print the version number and exit.
NOTES
usermod will not allow you to change the name, User ID or home directory of a user, which is logged in. usermod will not change the User ID
of running processes and not the ownership of crontab and at jobs.
FILES
/etc/group - group information
/etc/passwd - user account information
/etc/shadow - shadow user account information
SEE ALSO
passwd(1), login.defs(5), group(5), passwd(5), shadow(5), useradd(8), userdel(8)
AUTHOR
Thorsten Kukuk <kukuk@suse.de>
pwdutils Feb 2010 usermod(8)