It can be the name of a new user or the name of an existing user (or a user created before by newusers). In case of an existing user, the user's information will be changed, otherwise a new user will be created.
If the field is empty, a new (unused) UID will be defined automatically by newusers.
If this field contains a number, this number will be used as the UID.
If this field contains the name of an existing user (or the name of a user created before by newusers), the UID of the specified user will be used.
If the UID of an existing user is changed, the files ownership of the user's file should be fixed manually.
If this field contains the name of an existing group (or a group created before by newusers), the GID of this group will be used as the primary group ID for the user.
If this field is a number, this number will be used as the primary group ID of the user. If no groups exist with this GID, a new group will be created with this GID, and the name of the user.
If this field is empty, a new group will be created with the name of the user and a GID will be automatically defined by newusers to be used as the primary group ID for the user and as the GID for the new group.
If this field contains the name of a group which does not exist (and was not created before by newusers), a new group will be created with the specified name and a GID will be automatically defined by newusers to be used as the primary group ID for the user and GID for the new group.
If this field does not specify an existing directory, the specified directory is created, with ownership set to the user being created or updated and its primary group. Note that newusers does not create parent directories of the new user's home directory. The newusers command will fail to create the home directory if the parent directories do not exist, and will send a message to stderr informing the user of the failure. The newusers command will not halt or return a failure to the calling shell if it fails to create the home directory, it will continue to process the batch of new users specified.
If the home directory of an existing user is changed, newusers does not move or copy the content of the old directory to the new location. This should be done manually.
newusers first tries to create or change all the specified users, and then write these changes to the user or group databases. If an error occurs (except in the final writes to the databases), no changes are committed to the databases.
The options which apply to the newusers command are:
The available methods are DES, MD5, NONE, and SHA256 or SHA512 if your libc support these methods.
System users will be created with no aging information in /etc/shadow, and their numeric identifiers are chosen in the SYS_UID_MIN-SYS_UID_MAX range, defined in login.defs, instead of UID_MIN-UID_MAX (and their GID counterparts for the creation of groups).
-R, --root CHROOT_DIR
The value 0 means that the system will choose the default number of rounds for the crypt method (5000).
A minimal value of 1000 and a maximal value of 999,999,999 will be enforced.
You can only use this option with the SHA256 or SHA512 crypt method.
By default, the number of rounds is defined by the SHA_CRYPT_MIN_ROUNDS and SHA_CRYPT_MAX_ROUNDS variables in /etc/login.defs.
The input file must be protected since it contains unencrypted passwords.
The following configuration variables in /etc/login.defs change the behavior of this tool:
It can take one of these values: DES (default), MD5, SHA256, SHA512.
Note: this parameter overrides the MD5_CRYPT_ENAB variable.
GID_MAX (number), GID_MIN (number)
The default value for GID_MIN (resp. GID_MAX) is 1000 (resp. 60000).
useradd and newusers use this to set the mode of the home directory they create.
The default value is 0, meaning that there are no limits in the number of members in a group.
This feature (split group) permits to limit the length of lines in the group file. This is useful to make sure that lines for NIS groups are not larger than 1024 characters.
If you need to enforce such limit, you can use 25.
Note: split groups may not be supported by all tools (even in the Shadow toolsuite). You should not use this variable unless you really need it.
This variable is superseded by the ENCRYPT_METHOD variable or by any command line option used to configure the encryption algorithm.
This variable is deprecated. You should use ENCRYPT_METHOD.
SHA_CRYPT_MIN_ROUNDS (number), SHA_CRYPT_MAX_ROUNDS (number)
With a lot of rounds, it is more difficult to brute forcing the password. But note also that more CPU resources will be needed to authenticate users.
If not specified, the libc will choose the default number of rounds (5000).
The values must be inside the 1000-999,999,999 range.
If only one of the SHA_CRYPT_MIN_ROUNDS or SHA_CRYPT_MAX_ROUNDS values is set, then this value will be used.
If SHA_CRYPT_MIN_ROUNDS > SHA_CRYPT_MAX_ROUNDS, the highest value will be used.
SUB_GID_MIN (number), SUB_GID_MAX (number), SUB_GID_COUNT (number)
The default values for SUB_GID_MIN, SUB_GID_MAX, SUB_GID_COUNT are respectively 100000, 600100000 and 65536.
SUB_UID_MIN (number), SUB_UID_MAX (number), SUB_UID_COUNT (number)
The default values for SUB_UID_MIN, SUB_UID_MAX, SUB_UID_COUNT are respectively 100000, 600100000 and 65536.
SYS_GID_MAX (number), SYS_GID_MIN (number)
The default value for SYS_GID_MIN (resp. SYS_GID_MAX) is 101 (resp. GID_MIN-1).
SYS_UID_MAX (number), SYS_UID_MIN (number)
The default value for SYS_UID_MIN (resp. SYS_UID_MAX) is 101 (resp. UID_MIN-1).
UID_MAX (number), UID_MIN (number)
The default value for UID_MIN (resp. UID_MAX) is 1000 (resp. 60000).
useradd and newusers use this mask to set the mode of the home directory they create if HOME_MODE is not set.
It is also used by login to define users' initial umask. Note that this mask can be overridden by the user's GECOS line (if QUOTAS_ENAB is set) or by the specification of a limit with the K identifier in limits(5).