Install OpenCV 3.2 in Ubuntu 16.04 LTS (Linux)
In this post we will see How to install OpenCV in Ubuntu. OpenCV is an image processing library created by […]
Linux
Why Linux?
Linux is free
It’s fully customizable
It’s stable (i.e. it almost never crashes)
These characteristics make it an ideal OS for programmers and scientists.
Are you Curious about Linux, but not sure where to start ? Start here: “Linux : An Absolute Beginner’s Tutorial Guide” will teach you everything you need to know about Ubuntu in easy-to-understand language.
How to Install Redis On Ubuntu 16.04 LTS
In this post we will see How To Install Redis On Ubuntu Linux To install Redis, run the following commands: […]
Vim Cheat Sheet
The vi/vim Editor There are two versatile editors in UNIX – vi and emacs. vi is a full-screen editor. It […]
Bash Shell scripting – The case statement
The Case Statement The case statement is used to execute statements based on specific values. Often used in place of […]
Bash Shell scripting – Arithmetic Expressions in BASH
The Arithmetic expression is very important feature for performing number arithmetic operations in scripts. By default variables are treated as […]
How to kill a Process in Linux / UNIX Systems (Terminate Process in Linux)
To kill processes in Linux several options can be used. kill command The most important and frequently used option […]
Bash Shell scripting – Check if File Exists or Not
In this post we will see how to write a bash shell script to Check if File Exists or Not. This […]
Bash Shell scripting – If Statement ( If then fi, If then else fi, If elif else fi)
Bash Shell Conditional Statements Conditionals let us decide whether to perform an action or not, this decision is taken by evaluating […]
How to Install FFmpeg On Ubuntu 16.04 LTS
FFmpeg is a Complete cross-platform solution to record, convert, and stream media. In this post we will see how to […]
How To Install cURL on Ubuntu 16.04 LTS
In this post we will see How To Install curl on Ubuntu 16.04 using command line terminal. If you want […]
Bash Shell scripting – Read User Input
USER INPUT Read command – The read command allows you to prompt for input and store it in a variable. Read a […]
How To Install MySQL on Ubuntu 16.04 LTS
In this post we will learn how to How To Install MySQL on Ubuntu 16.04 LTS. The same procedure can be […]
Commonly used Linux commands
Command Explanation Example ls List files in directory; current directory is used if no directory is supplied $ ls ~/Desktop […]
Linux man page – useradd command
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 |
USERADD(8) System Management Commands USERADD(8) NAME useradd - create a new user or update default new user information SYNOPSIS useradd [options] LOGIN useradd -D useradd -D [options] DESCRIPTION useradd is a low level utility for adding users. On Debian, administrators should usually use adduser(8) instead. When invoked without the -D option, the useradd command creates a new user account using the values specified on the command line plus the default values from the system. Depending on command line options, the useradd command will update system files and may also create the new user's home directory and copy initial files. By default, a group will also be created for the new user (see -g, -N, -U, and USERGROUPS_ENAB). OPTIONS The options which apply to the useradd command are: -b, --base-dir BASE_DIR The default base directory for the system if -dHOME_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. -c, --comment COMMENT Any text string. It is generally a short description of the login, and is currently used as the field for the user's full name. -d, --home HOME_DIR The new user will be created using HOME_DIR as the value for the user's login directory. The default is to append the LOGIN name to BASE_DIR and use that as the login directory name. The directory HOME_DIR does not have to exist but will not be created if it is missing. -D, --defaults See below, the subsection "Changing the default values". -e, --expiredate EXPIRE_DATE The date on which the user account will be disabled. The date is specified in the format YYYY-MM-DD. If not specified, useradd will use the default expiry date specified by the EXPIRE variable in /etc/default/useradd, or an empty string (no expiry) by default. -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. -h, --help Display help message and exit. -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 ageing, 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 resetted to avoid reusing the entry from a previously deleted user. For the compatibility with previous Debian's useradd, the -O option is also supported. -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. -M 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 an 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. -s, --shell SHELL The name of the user's login shell. The default is to leave this field blank, which causes the system to select the default login shell specified by the SHELL variable in /etc/default/useradd, or an empty string by default. -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. It is usually recommended to only use usernames that begin with a lower case letter or an underscore, followed by lower case letters, digits, underscores, or dashes. They can end with a dollar sign. In regular expression terms: [a-z_][a-z0-9_-]*[$]? On Debian, the only constraints are that usernames must neither start with a dash ('-') nor plus ('+') nor tilde ('~') nor contain a colon (':'), a comma (','), or a whitespace (space: ' ', end of line: '\n', tabulation: '\t', etc.). Note that using a slash ('/') may break the default algorithm for the definition of the user's home directory. 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. 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. 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 pam_umask as the default umask value. USERGROUPS_ENAB (boolean) 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/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), userdel(8), usermod(8). shadow-utils 4.1.5.1 02/17/2014 USERADD(8) |
Linux man page – userdel command
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 |
USERDEL(8) System Management Commands USERDEL(8) NAME userdel - delete a user account and related files SYNOPSIS userdel [options] LOGIN DESCRIPTION userdel is a low level utility for removing users. On Debian, administrators should usually use deluser(8) instead. The userdel command modifies the system account files, deleting all entries that refer to the user name LOGIN. The named user must exist. OPTIONS The options which apply to the userdel command are: -f, --force This option forces the removal of the user account, even if the user is still logged in. It also forces userdel to remove the user's home directory and mail spool, even if another user uses the same home directory or if the mail spool is not owned by the specified user. If USERGROUPS_ENAB is defined to yes in /etc/login.defs and if a group exists with the same name as the deleted user, then this group will be removed, even if it is still the primary group of another user. Note: This option is dangerous and may leave your system in an inconsistent state. -h, --help Display help message and exit. -r, --remove Files in the user's home directory will be removed along with the home directory itself and the user's mail spool. Files located in other file systems will have to be searched for and deleted manually. The mail spool is defined by the MAIL_DIR variable in the login.defs file. -R, --root CHROOT_DIR Apply changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory. -Z, --selinux-user Remove any SELinux user mapping for the user's login. CONFIGURATION The following configuration variables in /etc/login.defs change the behavior of this tool: 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. 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. USERDEL_CMD (string) 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). The return code of the script is not taken into account. Here is an example script, which removes the user's cron, at and print jobs: #! /bin/sh # Check for the required argument. if [ $# != 1 ]; then echo "Usage: $0 username" exit 1 fi # Remove cron jobs. crontab -r -u $1 # Remove at jobs. # Note that it will remove any jobs owned by the same UID, # even if it was shared by a different username. AT_SPOOL_DIR=/var/spool/cron/atjobs find $AT_SPOOL_DIR -name "[^.]*" -type f -user $1 -delete \; # Remove print jobs. lprm $1 # All done. exit 0 USERGROUPS_ENAB (boolean) 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/group Group account information. /etc/login.defs Shadow password suite configuration. /etc/passwd User account information. /etc/shadow Secure user account information. EXIT VALUES The userdel command exits with the following values: 0 success 1 can't update password file 2 invalid command syntax 6 specified user doesn't exist 8 user currently logged in 10 can't update group file 12 can't remove home directory CAVEATS userdel will not allow you to remove an account if there are running processes which belong to this account. In that case, you may have to kill those processes or lock the user's password or account and remove the account later. The -f option can force the deletion of this account. You should manually check all file systems to ensure that no files remain owned by this user. You may not remove any NIS attributes on a NIS client. This must be performed on the NIS server. If USERGROUPS_ENAB is defined to yes in /etc/login.defs, userdel will delete the group with the same name as the user. To avoid inconsistencies in the passwd and group databases, userdel will check that this group is not used as a primary group for another user, and will just warn without deleting the group otherwise. The -f option can force the deletion of this group. SEE ALSO chfn(1), chsh(1), passwd(1), login.defs(5), gpasswd(8), groupadd(8), groupdel(8), groupmod(8), useradd(8), usermod(8). shadow-utils 4.1.5.1 02/17/2014 USERDEL(8) |