Comandos de la terminal/useradd
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useradd
[root@Llawyr ~]# ls -al $( which useradd )
-rwxr-xr-x 1 root root 119176 Oct 18 2013 /usr/sbin/useradd*
[root@Llawyr ~]# ls -al $( which adduser )
lrwxrwxrwx 1 root root 7 Sep 22 13:33 /usr/sbin/adduser -> useradd*
Useradd puede modificar /etc/passwd, /etc/shadow, /etc/gshadow y /etc/group.
También puede crear los carpetas de hogar y archivos spool de correo.
Su comportamiento se define mediante el archivo /etc/login.defs.
[root@Llawyr ~]# cat /etc/login.defs
# *REQUIRED*
# Directory where mailboxes reside, _or_ name of file, relative to the
# home directory. If you _do_ define both, MAIL_DIR takes precedence.
# QMAIL_DIR is for Qmail
#
#QMAIL_DIR Maildir
MAIL_DIR /var/spool/mail
#MAIL_FILE .mail
# Password aging controls:
#
# PASS_MAX_DAYS Maximum number of days a password may be used.
# PASS_MIN_DAYS Minimum number of days allowed between password changes.
# PASS_MIN_LEN Minimum acceptable password length.
# PASS_WARN_AGE Number of days warning given before a password expires.
#
PASS_MAX_DAYS 99999
PASS_MIN_DAYS 0
#PASS_MIN_LEN 5
PASS_WARN_AGE 7
#
# Min/max values for automatic uid selection in useradd
#
UID_MIN 500
UID_MAX 60000
#
# Min/max values for automatic gid selection in groupadd
#
GID_MIN 500
GID_MAX 60000
#
# If defined, this command is run when removing a user.
# It should remove any at/cron/print jobs etc. owned by
# the user to be removed (passed as the first argument).
#
# USERDEL_CMD /usr/sbin/userdel_local
#
# If useradd should create home directories for users by default
# On RH systems, we do. This option is ORed with the -m flag on
# useradd command line.
#
CREATE_HOME yes
#
# The password hashing method and iteration count to use for group
# passwords that may be set with gpasswd(1).
#
CRYPT_PREFIX $2a$
CRYPT_ROUNDS 8
#
# Whether to use tcb password shadowing scheme. Use 'yes' if using
# tcb and 'no' if using /etc/shadow
#
USE_TCB no
#
# Whether newly created tcb-style shadow files should be readable by
# group "auth".
#
TCB_AUTH_GROUP yes
#
# Whether useradd should create symlinks rather than directories under
# /etc/tcb for newly created accounts with UIDs over 1000. See tcb(5)
# for information on why this may be needed.
#
TCB_SYMLINKS no
#
# Delay in seconds before being allowed another attempt after a login failure
#
FAIL_DELAY 3
#
# Enable display of unknown usernames when login failures are recorded.
#
LOG_UNKFAIL_ENAB no
#
# Enable logging of successful logins
#
LOG_OK_LOGINS no
#
# Enable "syslog" logging of su activity - in addition to sulog file logging.
# SYSLOG_SG_ENAB does the same for newgrp and sg.
#
SYSLOG_SU_ENAB yes
SYSLOG_SG_ENAB yes
#
# If defined, either full pathname of a file containing device names or
# a ":" delimited list of device names. Root logins will be allowed only
# upon these devices.
#
CONSOLE /etc/securetty
#CONSOLE console:tty01:tty02:tty03:tty04
#
# If defined, the command name to display when running "su -". For
# example, if this is defined as "su" then a "ps" will display the
# command is "-su". If not defined, then "ps" would display the
# name of the shell actually being run, e.g. something like "-sh".
#
SU_NAME su
#
# If defined, file which inhibits all the usual chatter during the login
# sequence. If a full pathname, then hushed mode will be enabled if the
# user's name or shell are found in the file. If not a full pathname, then
# hushed mode will be enabled if the file exists in the user's home directory.
#
HUSHLOGIN_FILE .hushlogin
#HUSHLOGIN_FILE /etc/hushlogins
#
# *REQUIRED* The default PATH settings, for superuser and normal users.
#
# (they are minimal, add the rest in the shell startup files)
ENV_SUPATH PATH=/usr/local/sbin:/usr/sbin:/usr/local/bin:/usr/bin
ENV_PATH PATH=/usr/local/bin:/usr/bin
#
# Terminal permissions
#
# TTYGROUP Login tty will be assigned this group ownership.
# TTYPERM Login tty will be set to this permission.
#
# If you have a "write" program which is "setgid" to a special group
# which owns the terminals, define TTYGROUP to the group number and
# TTYPERM to 0620. Otherwise leave TTYGROUP commented out and assign
# TTYPERM to either 622 or 600.
#
TTYGROUP tty
TTYPERM 0600
#
# Login configuration initializations:
#
# ERASECHAR Terminal ERASE character ('\010' = backspace).
# KILLCHAR Terminal KILL character ('\025' = CTRL/U).
# UMASK Default "umask" value.
# ULIMIT Default "ulimit" value.
#
# The ERASECHAR and KILLCHAR are used only on System V machines.
# The ULIMIT is used only if the system supports it.
# (now it works with setrlimit too; ulimit is in 512-byte units)
#
# Prefix these values with "0" to get octal, "0x" to get hexadecimal.
#
ERASECHAR 0177
KILLCHAR 025
UMASK 022
#ULIMIT 2097152
#
# Max number of login retries if password is bad
#
LOGIN_RETRIES 5
#
# Max time in seconds for login
#
LOGIN_TIMEOUT 60
#
# Which fields may be changed by regular users using chfn - use
# any combination of letters "frwh" (full name, room number, work
# phone, home phone). If not defined, no changes are allowed.
# For backward compatibility, "yes" = "rwh" and "no" = "frwh".
#
CHFN_RESTRICT rwh
#
# Should login be allowed if we can't cd to the home directory?
# Default in no.
#
DEFAULT_HOME yes
#
# Enable setting of the umask group bits to be the same as owner bits
# (examples: 022 -> 002, 077 -> 007) for non-root users, if the uid is
# the same as gid, and username is the same as the primary group name.
#
# This also enables userdel to remove user groups if no members exist.
#
USERGROUPS_ENAB yes
[root@Llawyr ~]# useradd --help
Usage: useradd [options] LOGIN
useradd -D
useradd -D [options]
Options:
-b, --base-dir BASE_DIR base directory for the home directory of the
new account
-c, --comment COMMENT GECOS field of the new account
-d, --home-dir HOME_DIR home directory of the new account
-D, --defaults print or change default useradd configuration
-e, --expiredate EXPIRE_DATE expiration date of the new account
-f, --inactive INACTIVE password inactivity period of the new account
-g, --gid GROUP name or ID of the primary group of the new
account
-G, --groups GROUPS list of supplementary groups of the new
account
-h, --help display this help message and exit
-k, --skel SKEL_DIR use this alternative skeleton directory
-K, --key KEY=VALUE override /etc/login.defs defaults
-l, --no-log-init do not add the user to the lastlog and
faillog databases
-m, --create-home create the user's home directory
-M, --no-create-home do not create the user's home directory
-N, --no-user-group do not create a group with the same name as
the user
-o, --non-unique allow to create users with duplicate
(non-unique) UID
-p, --password PASSWORD encrypted password of the new account
-r, --system create a system account
-R, --root CHROOT_DIR directory to chroot into
-s, --shell SHELL login shell of the new account
-u, --uid UID user ID of the new account
-U, --user-group create a group with the same name as the user
[root@Llawyr ~]# rpm -qf $( which useradd )
shadow-utils-4.1.5.1-6.mga4
[root@Llawyr ~]# tail -n 5 /etc/passwd /etc/group /etc/shadow /etc/gshadow
==> /etc/passwd <==
gdm:x:486:477:system user for gdm:/var/lib/gdm:/bin/false
sshd:x:485:476:system user for openssh:/var/empty:/bin/true
chrony:x:484:475:system user for chrony:/var/lib/chrony:/sbin/nologin
nobody:x:65534:65534:Nobody:/:/bin/sh
rrc:x:500:500:Richard Couture:/home/rrc:/bin/bash
==> /etc/group <==
gdm:x:477:
sshd:x:476:
chrony:x:475:
lpadmin:x:474:
rrc:x:500:
==> /etc/shadow <==
lightdm:!:16335::::::
gdm:!:16335::::::
sshd:!:16335::::::
chrony:!:16335::::::
rrc:$2a$08$BlahBlahBlahjt6W:16335:0:99999:7:::
==> /etc/gshadow <==
gdm:!::
sshd:!::
chrony:!::
lpadmin:!::
rrc:!::
[root@Llawyr ~]# ls -al /home
total 28
drwxr-x--x 4 root adm 4096 Oct 16 12:01 ./
drwxr-xr-x 20 root adm 4096 Oct 14 10:24 ../
drwxr-x--x 2 root root 16384 Jul 29 05:50 lost+found/
drwxr-x--x 49 rrc rrc 4096 Oct 16 11:37 rrc/
[root@Llawyr ~]# useradd DelMe1
[root@Llawyr ~]# tail -n 5 /etc/passwd /etc/group /etc/shadow /etc/gshadow
==> /etc/passwd <==
sshd:x:485:476:system user for openssh:/var/empty:/bin/true
chrony:x:484:475:system user for chrony:/var/lib/chrony:/sbin/nologin
nobody:x:65534:65534:Nobody:/:/bin/sh
rrc:x:500:500:Richard Couture:/home/rrc:/bin/bash
DelMe1:x:501:501::/home/DelMe1:/bin/bash
==> /etc/group <==
sshd:x:476:
chrony:x:475:
lpadmin:x:474:
rrc:x:500:
DelMe1:x:501:
==> /etc/shadow <==
gdm:!:16335::::::
sshd:!:16335::::::
chrony:!:16335::::::
rrc:$2a$08$BlahBlahBlah:16335:0:99999:7:::
DelMe1:!:16359:0:99999:7:::
==> /etc/gshadow <==
sshd:!::
chrony:!::
lpadmin:!::
rrc:!::
DelMe1:!::
[root@Llawyr ~]# ls -al /home
total 32
drwxr-x--x 5 root adm 4096 Oct 16 15:40 ./
drwxr-xr-x 20 root adm 4096 Oct 14 10:24 ../
drwxr-xr-x 4 DelMe1 DelMe1 4096 Oct 16 15:40 DelMe1/
drwxr-x--x 2 root root 16384 Jul 29 05:50 lost+found/
drwxr-x--x 49 rrc rrc 4096 Oct 16 15:39 rrc/
[root@Llawyr ~]# useradd -c "Del Me 2" -s /usr/sbin/nologin -d /mnt/DelMe2 -G webmin DelMe2
[root@Llawyr ~]# tail -n 5 /etc/passwd /etc/group /etc/shadow /etc/gshadow
==> /etc/passwd <==
chrony:x:484:475:system user for chrony:/var/lib/chrony:/sbin/nologin
nobody:x:65534:65534:Nobody:/:/bin/sh
rrc:x:500:500:Richard Couture:/home/rrc:/bin/bash
DelMe1:x:501:501::/home/DelMe1:/bin/bash
DelMe2:x:502:502:Del Me 2:/mnt/DelMe2:/usr/sbin/nologin
==> /etc/group <==
chrony:x:475:
lpadmin:x:474:
rrc:x:500:
DelMe1:x:501:
DelMe2:x:502:
==> /etc/shadow <==
sshd:!:16335::::::
chrony:!:16335::::::
rrc:$2a$08$BlahBlahBlah:16335:0:99999:7:::
DelMe1:!:16359:0:99999:7:::
DelMe2:!:16359:0:99999:7:::
==> /etc/gshadow <==
chrony:!::
lpadmin:!::
rrc:!::
DelMe1:!::
DelMe2:!::
[root@Llawyr ~]# ls -al /mnt
total 12
drwxr-x--- 3 root adm 4096 Oct 16 15:44 ./
drwxr-xr-x 20 root adm 4096 Oct 14 10:24 ../
drwxr-xr-x 4 DelMe2 DelMe2 4096 Oct 16 15:44 DelMe2/
[root@Llawyr ~]# grep webmin /etc/group
webmin:x:417:rrc,DelMe2
EXIT VALUES
The useradd command exits with the following values:
0
success
1
can't update password file
2
invalid command syntax
3
invalid argument to option
4
UID already in use (and no -o)
6
specified group doesn't exist
9
username already in use
10
can't update group file
12
can't create home directory
14
can't update SELinux user mapping
