OPTIONS The options which apply to the useradd command are:
-b, --base-dir BASE_DIR
The default base directory for the system if -d HOME_DIR is not specified. BASE_DIR is concatenated with the account name to define
the home directory. If the -m option is not used, BASE_DIR must exist.
If this option is not specified, useradd will use the base directory specified by the HOME variable in /etc/default/useradd, or
/home by default.
# useradd defaults file
GROUP=100
HOME=/home
INACTIVE=-1
EXPIRE=
SHELL=/bin/bash
SKEL=/etc/skel
CREATE_MAIL_SPOOL=yes
-D, –defaults See below, the subsection “Changing the default values”.
-f, –inactive INACTIVE The number of days after a password expires until the account is permanently disabled. A value of 0 disables the account as soon as the password has expired, and a value of -1 disables the feature.
If not specified, useradd will use the default inactivity period specified by the INACTIVE variable in /etc/default/useradd, or -1
by default.
-g, --gid GROUP
The group name or number of the user's initial login group. The group name must exist. A group number must refer to an already existing group.
If not specified, the behavior of useradd will depend on the USERGROUPS_ENAB variable in /etc/login.defs. If this variable is set to
yes (or -U/--user-group is specified on the command line), a group will be created for the user, with the same name as her
loginname. If the variable is set to no (or -N/--no-user-group is specified on the command line), useradd will set the primary group
of the new user to the value specified by the GROUP variable in /etc/default/useradd, or 100 by default.
-G, --groups GROUP1[,GROUP2,...[,GROUPN]]]
A list of supplementary groups which the user is also a member of. Each group is separated from the next by a comma, with no
intervening whitespace. The groups are subject to the same restrictions as the group given with the -g option. The default is for
the user to belong only to the initial group.
-k, --skel SKEL_DIR
The skeleton directory, which contains files and directories to be copied in the user's home directory, when the home directory is created by useradd.
This option is only valid if the -m (or --create-home) option is specified.
If this option is not set, the skeleton directory is defined by the SKEL variable in /etc/default/useradd or, by default, /etc/skel.
If possible, the ACLs and extended attributes are copied.
-K, --key KEY=VALUE
Overrides /etc/login.defs defaults (UID_MIN, UID_MAX, UMASK, PASS_MAX_DAYS and others).
Example: -K PASS_MAX_DAYS=-1 can be used when creating system account to turn off password aging, even though system account has no
password at all. Multiple -K options can be specified, e.g.: -K UID_MIN=100 -K UID_MAX=499
-l, --no-log-init
Do not add the user to the lastlog and faillog databases.
By default, the user's entries in the lastlog and faillog databases are reset to avoid reusing the entry from a previously deleted user.
-m, --create-home
Create the user's home directory if it does not exist. The files and directories contained in the skeleton directory (which can be defined with the -k option) will be copied to the home directory.
By default, if this option is not specified and CREATE_HOME is not enabled, no home directories are created.
The directory where the user's home directory is created must exist and have proper SELinux context and permissions. Otherwise the
user's home directory cannot be created or accessed.
-M, --no-create-home
Do no create the user's home directory, even if the system wide setting from /etc/login.defs (CREATE_HOME) is set to yes.
-N, --no-user-group
Do not create a group with the same name as the user, but add the user to the group specified by the -g option or by the GROUP variable in /etc/default/useradd.
The default behavior (if the -g, -N, and -U options are not specified) is defined by the USERGROUPS_ENAB variable in /etc/login.defs.
-o, --non-unique
Allow the creation of a user account with a duplicate (non-unique) UID.
This option is only valid in combination with the -u option.
-p, --password PASSWORD
The encrypted password, as returned by crypt(3). The default is to disable the password.
Note: This option is not recommended because the password (or encrypted password) will be visible by users listing the processes.
You should make sure the password respects the system's password policy.
-r, --system
Create a system account.
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 /etc/login.defs, instead of UID_MIN-UID_MAX (and their GID counterparts for the creation of groups).
Note that useradd will not create a home directory for such a user, regardless of the default setting in /etc/login.defs (CREATE_HOME). You have to specify the -m options if you want a home directory for a system account to be created.
-R, --root CHROOT_DIR
Apply changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory.
-P, --prefix PREFIX_DIR
Apply changes in the PREFIX_DIR directory and use the configuration files from the PREFIX_DIR directory. This option does not chroot and is intended for preparing a cross-compilation target. Some limitations: NIS and LDAP users/groups are not verified. PAM authentication is using the host files. No SELINUX support.
-u, –uid UID The numerical value of the user’s ID. This value must be unique, unless the -o option is used. The value must be non-negative. The default is to use the smallest ID value greater than or equal to UID_MIN and greater than every other user.
See also the -r option and the UID_MAX description.
-U, --user-group
Create a group with the same name as the user, and add the user to this group.
The default behavior (if the -g, -N, and -U options are not specified) is defined by the USERGROUPS_ENAB variable in
/etc/login.defs.
-Z, --selinux-user SEUSER
The SELinux user for the user's login. The default is to leave this field blank, which causes the system to select the default
SELinux user.
Changing the default values When invoked with only the -D option, useradd will display the current default values. When invoked with -D plus other options, useradd will update the default values for the specified options. Valid default-changing options are:
-b, --base-dir BASE_DIR
The path prefix for a new user's home directory. The user's name will be affixed to the end of BASE_DIR to form the new user's home
directory name, if the -d option is not used when creating a new account.
This option sets the HOME variable in /etc/default/useradd.
-e, --expiredate EXPIRE_DATE
The date on which the user account is disabled.
This option sets the EXPIRE variable in /etc/default/useradd.
-f, --inactive INACTIVE
The number of days after a password has expired before the account will be disabled.
This option sets the INACTIVE variable in /etc/default/useradd.
-g, --gid GROUP
The group name or ID for a new user's initial group (when the -N/--no-user-group is used or when the USERGROUPS_ENAB variable is set
to no in /etc/login.defs). The named group must exist, and a numerical group ID must have an existing entry.
This option sets the GROUP variable in /etc/default/useradd.
-s, --shell SHELL
The name of a new user's login shell.
This option sets the SHELL variable in /etc/default/useradd.
NOTES The system administrator is responsible for placing the default user files in the /etc/skel/ directory (or any other skeleton directory specified in /etc/default/useradd or on the command line).
CAVEATS You may not add a user to a NIS or LDAP group. This must be performed on the corresponding server.
Similarly, if the username already exists in an external user database such as NIS or LDAP, useradd will deny the user account creation request.
Usernames may contain only lower and upper case letters, digits, underscores, or dashes. They can end with a dollar sign. Dashes are not allowed at the beginning of the username. Fully numeric usernames and usernames . or .. are also disallowed. It is not recommended to use usernames beginning with . character as their home directories will be hidden in the ls output. In regular expression terms:
[a-zA-Z0-9_.][a-zA-Z0-9_.-]*[$]?
Usernames may only be up to 32 characters long.
CONFIGURATION The following configuration variables in /etc/login.defs change the behavior of this tool:
CREATE_HOME (boolean)
Indicate if a home directory should be created by default for new users.
This setting does not apply to system users, and can be overridden on the command line.
GID_MAX (number), GID_MIN (number)
Range of group IDs used for the creation of regular groups by useradd, groupadd, or newusers.
The default value for GID_MIN (resp. GID_MAX) is 1000 (resp. 60000).
MAIL_DIR (string)
The mail spool directory. This is needed to manipulate the mailbox when its corresponding user account is modified or deleted. If
not specified, a compile-time default is used.
MAIL_FILE (string)
Defines the location of the users mail spool files relatively to their home directory.
The MAIL_DIR and MAIL_FILE variables are used by useradd, usermod, and userdel to create, move, or delete the user's mail spool.
If MAIL_CHECK_ENAB is set to yes, they are also used to define the MAIL environment variable.
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.
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.
SUB_GID_MIN (number), SUB_GID_MAX (number), SUB_GID_COUNT (number)
If /etc/subuid exists, the commands useradd and newusers (unless the user already have subordinate group IDs) allocate SUB_GID_COUNT
unused group IDs from the range SUB_GID_MIN to SUB_GID_MAX for each new user.
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)
If /etc/subuid exists, the commands useradd and newusers (unless the user already have subordinate user IDs) allocate SUB_UID_COUNT
unused user IDs from the range SUB_UID_MIN to SUB_UID_MAX for each new user.
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)
Range of group IDs used for the creation of system groups by useradd, groupadd, or newusers.
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)
Range of user IDs used for the creation of system users by useradd or newusers.
The default value for SYS_UID_MIN (resp. SYS_UID_MAX) is 101 (resp. UID_MIN-1).
UID_MAX (number), UID_MIN (number)
Range of user IDs used for the creation of regular users by useradd or newusers.
The default value for UID_MIN (resp. UID_MAX) is 1000 (resp. 60000).
UMASK (number)
The file mode creation mask is initialized to this value. If not specified, the mask will be initialized to 022.
useradd and newusers use this mask to set the mode of the home directory they create
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).
USERGROUPS_ENAB (boolean)
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.
If set to yes, userdel will remove the user's group if it contains no more members, and useradd will create by default a group with
the name of the user.
FILES /etc/passwd User account information.
/etc/shadow
Secure user account information.
/etc/group
Group account information.
/etc/gshadow
Secure group account information.
/etc/default/useradd
Default values for account creation.
/etc/skel/
Directory containing default files.
/etc/subgid
Per user subordinate group IDs.
/etc/subuid
Per user subordinate user IDs.
/etc/login.defs
Shadow password suite configuration.
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
SEE ALSO chfn(1), chsh(1), passwd(1), crypt(3), groupadd(8), groupdel(8), groupmod(8), login.defs(5), newusers(8), subgid(5), subuid(5),userdel(8), usermod(8).
$ curl https://mirrors.edge.kernel.org/pub/linux/kernel/v2.4/linux-2.4.32.tar.gz -O % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 1 36.7M 1 575k 0 0 17431 0 0:36:50 0:00:33 0:36:17 27222
需要授权的网站
部分网站可能需要访问的授权，此时可以使用-u选项提供用户名和密码进行授权：
1 2
$ curl -u username https://www.website.com/ Enter host password for user 'username':
$ diff a b -y This is a. | This is b. Hello a. | Hello b. Hello World. Hello World. > One more line.
那么：
“|”表示前后2个文件内容有不同；
“<”表示后面文件比前面文件少了1行内容
“>”表示后面文件比前面文件多了1行内容
context模式比较
这种模式会输出所有的文件内容，并显示不同之处，还包括具体的时间。
如下*** 表示a的内容，--- 表示b的内容。
1 2 3 4 5 6 7 8 9 10 11 12 13
$ diff a b -c *** a 2013-03-04 23:20:20.322345200 +0800 --- b 2013-03-04 23:26:30.712130000 +0800 *************** *** 1,3 **** ! This is a. ! Hello a. Hello World. --- 1,4 ---- ! This is b. ! Hello b. Hello World. + One more line.
unified模式比较
这种模式会混合输出所有的文件内容，并显示不同之处，还包括具体的时间。
如下--- 表示a的内容，+++ 表示b的内容。
1 2 3 4 5 6 7 8 9 10
$ diff a b -u --- a 2013-03-04 23:20:20.322345200 +0800 --- b 2013-03-04 23:26:30.712130000 +0800 @@ -1,3 +1,4 @@ -This is a. -Hello a. +This is b. +Hello b. Hello World. +One more line.
对比时忽略空格
1 2 3 4 5
# diff -w name_list.txt name_list_new.txt
2c2,3 < John Doe --- > John M Doe > Jason Bourne
快速找出两个目录的不同
diff命令会按行比较文件。但是它也可以比较两个目录：
1 2 3 4
ls -l /tmp/r ls -l /tmp/s # 使用 diff 比较两个文件夹 diff /tmp/r/ /tmp/s/
$ diff a b -y This is a. | This is b. Hello a. | Hello b. Hello World. Hello World. > One more line.
那么：
“|”表示前后2个文件内容有不同；
“<”表示后面文件比前面文件少了1行内容
“>”表示后面文件比前面文件多了1行内容
context模式比较
这种模式会输出所有的文件内容，并显示不同之处，还包括具体的时间。
如下*** 表示a的内容，--- 表示b的内容。
1 2 3 4 5 6 7 8 9 10 11 12 13
$ diff a b -c *** a 2013-03-04 20:30:20.322345200 +0800 +++ b 2013-03-04 20:26:30.712130000 +0800 *************** *** 1,3 **** ! This is a. ! Hello a. Hello World. --- 1,4 ---- ! This is b. ! Hello b. Hello World. + One more line.
unified模式比较
这种模式会混合输出所有的文件内容，并显示不同之处，还包括具体的时间。
如下--- 表示a的内容，+++ 表示b的内容。
1 2 3 4 5 6 7 8 9 10
$ diff a b -u --- a 2013-03-04 20:30:20.322345200 +0800 +++ b 2013-03-04 20:26:30.712130000 +0800 @@ -1,3 +1,4 @@ -This is a. -Hello a. +This is b. +Hello b. Hello World. +One more line.
Mandatory arguments to long options are mandatory for short options too.
--normal
output a normal diff (the default)
-q, --brief
report only when files differ
-s, --report-identical-files
report when two files are the same
-c, -C NUM, --context[=NUM]
output NUM (default 3) lines of copied context
-e, --ed
output an ed script
-n, --rcs
output an RCS format diff
-W, --width=NUM
output at most NUM (default 130) print columns
--left-column
output only the left column of common lines
--suppress-common-lines
do not output common lines
-p, --show-c-function
show which C function each change is in
-F, --show-function-line=RE
show the most recent line matching RE
--label LABEL
use LABEL instead of file name and timestamp (can be repeated)
-t, --expand-tabs
expand tabs to spaces in output
-T, --initial-tab
make tabs line up by prepending a tab
--tabsize=NUM
tab stops every NUM (default 8) print columns
--suppress-blank-empty
suppress space or tab before empty output lines
-l, --paginate
pass output through 'pr' to paginate it
-r, --recursive
recursively compare any subdirectories found
--no-dereference
don't follow symbolic links
-N, --new-file
treat absent files as empty
--unidirectional-new-file
treat absent first files as empty
--ignore-file-name-case
ignore case when comparing file names
--no-ignore-file-name-case
consider case when comparing file names
-x, --exclude=PAT
exclude files that match PAT
-X, --exclude-from=FILE
exclude files that match any pattern in FILE
-S, --starting-file=FILE
start with FILE when comparing directories
--from-file=FILE1
compare FILE1 to all operands; FILE1 can be a directory
--to-file=FILE2
compare all operands to FILE2; FILE2 can be a directory
-i, --ignore-case
ignore case differences in file contents
-E, --ignore-tab-expansion
ignore changes due to tab expansion
-Z, --ignore-trailing-space
ignore white space at line end
-b, --ignore-space-change
ignore changes in the amount of white space
-w, --ignore-all-space
ignore all white space
-B, --ignore-blank-lines
ignore changes where lines are all blank
-I, --ignore-matching-lines=RE
ignore changes where all lines match RE
-a, --text
treat all files as text
--strip-trailing-cr
strip trailing carriage return on input
-D, --ifdef=NAME
output merged file with '#ifdef NAME' diffs
--GTYPE-group-format=GFMT
format GTYPE input groups with GFMT
--line-format=LFMT
format all input lines with LFMT
These format options provide fine-grained control over the output
of diff, generalizing -D/--ifdef.
LTYPE is 'old', 'new', or 'unchanged'.
GTYPE is LTYPE or 'changed'.
GFMT (only) may contain:
%< lines from FILE1
%> lines from FILE2
%= lines common to FILE1 and FILE2
%[-][WIDTH][.[PREC]]{doxX}LETTER
printf-style spec for LETTER
LETTERs are as follows for new group, lower case for old group:
F first line number
L last line number
N number of lines = L-F+1
E F-1
M L+1
%(A=B?T:E)
if A equals B then T else E
LFMT (only) may contain:
%L contents of line
%l contents of line, excluding any trailing newline
%[-][WIDTH][.[PREC]]{doxX}n
printf-style spec for input line number
Both GFMT and LFMT may contain:
%% %
%c'C' the single character C
%c'\OOO'
the character with octal code OOO
C the character C (other characters represent themselves)
-d, --minimal
try hard to find a smaller set of changes
--horizon-lines=NUM
keep NUM lines of the common prefix and suffix
--speed-large-files
assume large files and many scattered small changes
--color[=WHEN]
colorize the output; WHEN can be 'never', 'always', or 'auto' (the default)
--palette=PALETTE
the colors to use when --color is active; PALETTE is a colon-separated list of terminfo capabilities
FILES are 'FILE1 FILE2' or 'DIR1 DIR2' or 'DIR FILE' or 'FILE DIR'. If --from-file or --to-file is given,
there are no restrictions on FILE(s). If a FILE is '-', read standard input. Exit status is 0 if inputs are
the same, 1 if different, 2 if trouble.