[Ilugc] .a-tip-a-day. (grep - find lines matching pattern)
- From: raju.rajsand@xxxxxxxxx (Rajagopal Swaminathan)
- Date: Mon Nov 9 14:35:13 2009
Greetings,
On Mon, Nov 9, 2009 at 12:04 PM, Girish Venkatachalam
<girishvenkatachalam@xxxxxxxxx> wrote:
$ grep girish /etc/passwd
is known. grep stands for "global regular expression print"
AAAH....., isn't grep (and its derivatives) a nice can of worms (nicer
ones with regexps...) ;-)
ok, That being said, i would suggest one more stuff like newusers
esp.for bulk user adds...
[quote]
NEWUSERS(8) System Management Commands NEWUSERS(8)
NAME
newusers - update and create new users in batch
SYNOPSIS
newusers [new_users]
DESCRIPTION
The newusers command reads a file of user name and clear-text password
pairs and uses this information to update a group of existing users or
to create new users. Each line is in the same format as the standard
password file (see passwd(5)) with the following exceptions:
pw_passwd
This field will be encrypted and used as the new value of the
encrypted password.
pw_gid
This field must contain the name (or number) of a group. The user
will be added as a member to this group. When a non-existent group
name or number is specified, a new group will be created. In the
case of a non-existent group number, both the name and the number
of the new group will be this number.
pw_dir
This field will be checked for existence as a directory, and a new
directory with this name will be created if it does not already
exist. The ownership of the directory will be set to be that of the
user being created or updated.
This command is intended to be used in a large system environment where
many accounts are updated at a single time.
OPTIONS
The options which apply to the newusers command are:
-c, --crypt-method
Use the specified method to encrypt the passwords.
The available methods are DES, MD5, NONE, and SHA256 or SHA512 if
your libc support these methods.
-r, --system
Create a system account.
System users will be created with no aging information in
/etc/shadow, and their numeric identifiers are choosen 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).
-s, --sha-rounds
Use the specified number of rounds to encrypt the passwords.
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.
CAVEATS
The input file must be protected since it contains unencrypted
passwords.
PAM is not used to update the passwords. Only /etc/passwd and
/etc/shadow are updated, and the various checks or options provided by
PAM modules are not used.
CONFIGURATION
The following configuration variables in /etc/login.defs change the
behavior of this tool:
ENCRYPT_METHOD (string)
This defines the system default encryption algorithm for encrypting
passwords (if no algorithm are specified on the command line).
It can take one of these values:
DES (default)
MD5
SHA256
SHA512
Note: this parameter overrides the MD5_CRYPT_ENAB variable.
Note: if you use PAM, it is recommended to set this variable
consistently with the PAM modules configuration.
GID_MAX (number), GID_MIN (number)
Range of group IDs used for the creation of regular groups by
useradd, useradd, or newusers.
MAX_MEMBERS_PER_GROUP (number)
Maximum members per group entry. When the maximum is reached, a new
group entry (line) is started in /etc/group (with the same name,
same password, and same GID).
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.
MD5_CRYPT_ENAB (boolean)
Indicate if passwords must be encrypted using the MD5-based
algorithm. If set to yes, new passwords will be encrypted using the
MD5-based algorithm compatible with the one used by recent releases
of FreeBSD. It supports passwords of unlimited length and longer
salt strings. Set to no if you need to copy encrypted passwords to
other systems which dont understand the new algorithm. Default is
no.
This variable is superceded 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.
Note: if you use PAM, it is recommended to set this variable
consistently with the PAM modules configuration.
PASS_MAX_DAYS (number)
The maximum number of days a password may be used. If the password
is older than this, a password change will be forced. If not
specified, -1 will be assumed (which disables the restriction).
PASS_MIN_DAYS (number)
The minimum number of days allowed between password changes. Any
password changes attempted sooner than this will be rejected. If
not specified, -1 will be assumed (which disables the restriction).
PASS_WARN_AGE (number)
The number of days warning given before a password expires. A zero
means warning is given only upon the day of expiration, a negative
value means no warning is given. If not specified, no warning will
be provided.
SHA_CRYPT_MIN_ROUNDS (number), SHA_CRYPT_MAX_ROUNDS (number)
When ENCRYPT_METHOD is set to SHA256 or SHA512, this defines the
number of SHA rounds used by the encryption algorithm by default
(when the number of rounds is not specified on the command line).
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 1000-999999999 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.
SYS_GID_MAX (number), SYS_GID_MIN (number)
Range of group IDs used for the creation of system groups by
useradd, groupadd, or newusers.
SYS_UID_MAX (number), SYS_UID_MIN (number)
Range of user IDs used for the creation of system users by useradd
or newusers.
UID_MAX (number), UID_MIN (number)
Range of user IDs used for the creation of regular users by useradd
or newusers.
UMASK (number)
The permission mask is initialized to this value. If not specified,
the permission mask will be initialized to 022.
FILES
/etc/passwd
User account information.
/etc/shadow
Secure user account information.
/etc/group
Group account information.
/etc/gshadow
Secure group account information.
/etc/login.defs
Shadow password suite configuration.
SEE ALSO
login.defs(5), passwd(1), useradd(8).
System Management Commands 04/04/2009 NEWUSERS(8)
[unquote]
Thanks and regards,
Rajagopal
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