linux 新建用户配置文件 /etc/login.defs 简介

傷城~ 2021-08-28 23:02 516阅读 0赞

/etc/login.defs 是设置用户帐号限制的文件。该文件里的配置对root用户无效。/etc/login.defs 文件用于在Linux创建用户时，对用户的一些基本属性做默认设置，例如指定用户 UID 和 GID 的范围，用户的过期时间，密码的最大长度，等等。

需要注意的是，该文件的用户默认配置对 root 用户无效。并且，当此文件中的配置与 /etc/passwd 和 /etc/shadow 文件中的用户信息有冲突时，系统会以/etc/passwd 和 /etc/shadow 为准。

如果/etc/shadow文件里有相同的选项，则以/etc/shadow里的设置为准，也就是说/etc/shadow的配置优先级高于/etc/login.defs

![Linux新建用户配置文件 /etc/login.defs 详解][Linux_ _etc_login.defs]

读者可自行使用 vim /etc/login.defs 命令查看该文件中的内容，表 1 中对文件中的各个选项做出了具体的解释。

<table>  表 1 /etc/login.defs文件内容  
 <tbody> 
  <tr> 
   <th>设置项</th> 
   <th>含义</th> 
  </tr> 
  <tr> 
   <td>MAIL_DIR /var/spool/mail&nbsp;</td> 
   <td>创建用户时，系统会在目录 /var/spool/mail 中创建一个用户邮箱，比如 lamp 用户的邮箱是 /var/spool/mail/lamp。</td> 
  </tr> 
  <tr> 
   <td>PASS_MAX_DAYS 99999</td> 
   <td>密码有效期，99999 是自 1970 年 1 月 1 日起密码有效的天数，相当于 273 年，可理解为密码始终有效。</td> 
  </tr> 
  <tr> 
   <td>PASS_MIN_DAYS 0</td> 
   <td>表示自上次修改密码以来，最少隔多少天后用户才能再次修改密码，默认值是 0。</td> 
  </tr> 
  <tr> 
   <td>PASS_MIN_LEN 5</td> 
   <td>指定密码的最小长度，默认不小于&nbsp;5 位，但是现在用户登录时验证已经被 PAM 模块取代，所以这个选项并不生效。</td> 
  </tr> 
  <tr> 
   <td>PASS_WARN_AGE 7</td> 
   <td>指定在密码到期前多少天，系统就开始通过用户密码即将到期，默认为 7 天。</td> 
  </tr> 
  <tr> 
   <td>UID_MIN 500&nbsp;</td> 
   <td>指定最小 UID 为 500，也就是说，添加用户时，默认 UID 从 500 开始。注意，如果手工指定了一个用户的 UID 是 550，那么下一个创建的用户的 UID 就会从 551 开始，哪怕 500~549 之间的 UID 没有使用。</td> 
  </tr> 
  <tr> 
   <td>UID_MAX 60000</td> 
   <td>指定用户最大的 UID 为 60000。</td> 
  </tr> 
  <tr> 
   <td>GID_MIN 500</td> 
   <td>指定最小 GID 为 500，也就是在添加组时，组的 GID 从 500 开始。</td> 
  </tr> 
  <tr> 
   <td>GID_MAX 60000</td> 
   <td>用户 GID 最大为 60000。</td> 
  </tr> 
  <tr> 
   <td>CREATE_HOME yes</td> 
   <td>指定在创建用户时，是否同时创建用户主目录，yes 表示创建，no 则不创建，默认是 yes。</td> 
  </tr> 
  <tr> 
   <td>UMASK 077</td> 
   <td>用户主目录的权限默认设置为 077。</td> 
  </tr> 
  <tr> 
   <td>USERGROUPS_ENAB yes</td> 
   <td>指定删除用户的时候是否同时删除用户组，准备地说，这里指的是删除用户的初始组，此项的默认值为 yes。</td> 
  </tr> 
  <tr> 
   <td>ENCRYPT_METHOD SHA512</td> 
   <td>指定用户密码采用的加密规则，默认采用 SHA512，这是新的密码加密模式，原先的 Linux 只能用 DES 或 MD5 加密。</td> 
  </tr> 
 </tbody> 
</table>

/etc/login.defs 完整文件如下：

root@linuxidc:/home/linuxidc/linuxidc.com# cat /etc/login.defs
    #
    # /etc/login.defs - Configuration control definitions for the login package.
    #
    # Three items must be defined:  MAIL_DIR, ENV_SUPATH, and ENV_PATH.
    # If unspecified, some arbitrary (and possibly incorrect) value will
    # be assumed.  All other items are optional - if not specified then
    # the described action or option will be inhibited.
    #
    # Comment lines (lines beginning with "#") and blank lines are ignored.
    #
    # Modified for Linux.  --marekm
    
    # REQUIRED for useradd/userdel/usermod
    #  Directory where mailboxes reside, _or_ name of file, relative to the
    #  home directory.  If you _do_ define MAIL_DIR and MAIL_FILE,
    #  MAIL_DIR takes precedence.
    #
    #  Essentially:
    #      - MAIL_DIR defines the location of users mail spool files
    #        (for mbox use) by appending the username to MAIL_DIR as defined
    #        below.
    #      - MAIL_FILE defines the location of the users mail spool files as the
    #        fully-qualified filename obtained by prepending the user home
    #        directory before $MAIL_FILE
    #
    # NOTE: This is no more used for setting up users MAIL environment variable
    #      which is, starting from shadow 4.0.12-1 in Debian, entirely the
    #      job of the pam_mail PAM modules
    #      See default PAM configuration files provided for
    #      login, su, etc.
    #
    # This is a temporary situation: setting these variables will soon
    # move to /etc/default/useradd and the variables will then be
    # no more supported
    MAIL_DIR        /var/mail #创建用户时，要在目录/var/spool/mail中创建一个用户mail文件；
    #MAIL_FILE      .mail
    
    #
    # Enable logging and display of /var/log/faillog login failure info.
    # This option conflicts with the pam_tally PAM module.
    #
    FAILLOG_ENAB  yes #登录错误记录到日志
    
    #
    # Enable display of unknown usernames when login failures are recorded.
    #
    # WARNING: Unknown usernames may become world readable.
    # See #290803 and #298773 for details about how this could become a security
    # concern
    LOG_UNKFAIL_ENAB no #在建立用户时是否创建邮箱
    
    #
    # 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 #当限定超级用户管理日志时使用。
    SYSLOG_SG_ENAB  yes #当限定超级用户组管理日志时使用
    
    #
    # If defined, all su activity is logged to this file.
    #
    #SULOG_FILE /var/log/sulog
    
    #
    # If defined, file which maps tty line to TERM environment parameter.
    # Each line of the file is in a format something like "vt100  tty01".
    #
    #TTYTYPE_FILE /etc/ttytype
    
    #
    # If defined, login failures will be logged here in a utmp format
    # last, when invoked as lastb, will read /var/log/btmp, so...
    #
    FTMP_FILE /var/log/btmp
    
    #
    # 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 #使用户在使用su命令后用ps查看相关进程时显示的是-su而不是-sh。
    
    #
    # 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 #打开该选项可以掩盖登录信息,也就是在login(登录)过程中不显示/etc/motd中的信息。
    #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/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
    ENV_PATH PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
    
    #
    # 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.
    #
    # In Debian /usr/bin/bsd-write or similar programs are setgid tty
    # However, the default and recommended value for TTYPERM is still 0600
    # to not allow anyone to write to anyone else console or terminal
    
    # Users can still allow other people to write them by issuing
    # the "mesg y" command.
    
    TTYGROUP tty
    TTYPERM  0600  #设置用户登陆时的tty权限。
    
    #
    # Login configuration initializations:
    #
    # ERASECHAR Terminal ERASE character ('\010' = backspace).
    # KILLCHAR Terminal KILL character ('\025' = CTRL/U).
    # UMASK  Default "umask" value.
    #
    # The ERASECHAR and KILLCHAR are used only on System V machines.
    #
    # UMASK is the default umask value for pam_umask and is used by
    # useradd and newusers to set the mode of the new home directories.
    # 022 is the "historical" value in Debian for UMASK
    # 027, or even 077, could be considered better for privacy
    # There is no One True Answer here : each sysadmin must make up his/her
    # mind.
    #
    # If USERGROUPS_ENAB is set to "yes", that will modify this UMASK default value
    # for private user groups, i. e. the uid is the same as gid, and username is
    # the same as the primary group name: for these, the user permissions will be
    # used as group permissions, e. g. 022 will become 002.
    #
    # Prefix these values with "0" to get octal, "0x" to get hexadecimal.
    #
    ERASECHAR 0177
    KILLCHAR 025
    UMASK  022
    
    #
    # 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_WARN_AGE Number of days warning given before a password expires.
    #
    PASS_MAX_DAYS 99999 #用户的密码不过期最多的天数；
    PASS_MIN_DAYS 0 #密码修改之间最小的天数；
    PASS_WARN_AGE 7 #密码失效前多少天在用户登录时通知用户修改密码
    
    #
    # Min/max values for automatic uid selection in useradd
    #
    UID_MIN    1000 #最小UID为1000，也就是说添加用户时，UID是从1000开始的；
    UID_MAX   60000 #最大UID为60000；
    # System accounts
    #SYS_UID_MIN    100
    #SYS_UID_MAX    999
    
    #
    # Min/max values for automatic gid selection in groupadd
    #
    GID_MIN    1000 #最小用户组ID号
    GID_MAX   60000 #最大用户组ID
    # System accounts
    #SYS_GID_MIN    100
    #SYS_GID_MAX    999
    
    #
    # Max number of login retries if password is bad. This will most likely be
    # overriden by PAM, since the default pam_unix module has it's own built
    # in of 3 retries. However, this is a safe fallback in case you are using
    # an authentication module that does not enforce PAM_MAXTRIES.
    #
    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 #是否创用户家目录，要求创建；
    
    #
    # 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
    
    #
    # 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.
    #
    USERGROUPS_ENAB yes
    
    #
    # Instead of the real user shell, the program specified by this parameter
    # will be launched, although its visible name (argv[0]) will be the shell's.
    # The program may do whatever it wants (logging, additional authentification,
    # banner, ...) before running the actual shell.
    #
    # FAKE_SHELL /bin/fakeshell
    
    #
    # 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.
    #
    # This variable is used by login and su.
    #
    #CONSOLE /etc/consoles
    #CONSOLE console:tty01:tty02:tty03:tty04
    
    #
    # List of groups to add to the user's supplementary group set
    # when logging in on the console (as determined by the CONSOLE
    # setting).  Default is none.
    #
    # Use with caution - it is possible for users to gain permanent
    # access to these groups, even when not logged in on the console.
    # How to do it is left as an exercise for the reader...
    #
    # This variable is used by login and su.
    #
    #CONSOLE_GROUPS  floppy:audio:cdrom
    
    #
    # 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 don't understand the new algorithm.  Default is "no".
    #
    # This variable is deprecated. You should use ENCRYPT_METHOD.
    #
    #MD5_CRYPT_ENAB no
    
    #
    # If set to MD5 , MD5-based algorithm will be used for encrypting password
    # If set to SHA256, SHA256-based algorithm will be used for encrypting password
    # If set to SHA512, SHA512-based algorithm will be used for encrypting password
    # If set to DES, DES-based algorithm will be used for encrypting password (default)
    # Overrides the MD5_CRYPT_ENAB option
    #
    # Note: It is recommended to use a value consistent with
    # the PAM modules configuration.
    #
    ENCRYPT_METHOD SHA512 #加密模式
    
    #
    # Only used if ENCRYPT_METHOD is set to SHA256 or SHA512.
    #
    # Define the number of SHA rounds.
    # With a lot of rounds, it is more difficult to brute forcing the password.
    # But note also that it 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 MIN or MAX values is set, then this value will be used.
    # If MIN > MAX, the highest value will be used.
    #
    # SHA_CRYPT_MIN_ROUNDS 5000
    # SHA_CRYPT_MAX_ROUNDS 5000
    
    ################# OBSOLETED BY PAM ##############
    #      #
    # These options are now handled by PAM. Please #
    # edit the appropriate file in /etc/pam.d/ to #
    # enable the equivelants of them.
    #
    ###############
    
    #MOTD_FILE
    #DIALUPS_CHECK_ENAB
    #LASTLOG_ENAB
    #MAIL_CHECK_ENAB
    #OBSCURE_CHECKS_ENAB
    #PORTTIME_CHECKS_ENAB
    #SU_WHEEL_ONLY
    #CRACKLIB_DICTPATH
    #PASS_CHANGE_TRIES
    #PASS_ALWAYS_WARN
    #ENVIRON_FILE
    #NOLOGINS_FILE
    #ISSUE_FILE
    #PASS_MIN_LEN
    #PASS_MAX_LEN
    #ULIMIT
    #ENV_HZ
    #CHFN_AUTH
    #CHSH_AUTH
    #FAIL_DELAY
    
    ################# OBSOLETED #######################
    #        #
    # These options are no more handled by shadow.    #
    #                                                #
    # Shadow utilities will display a warning if they #
    # still appear.                                  #
    #                                                #
    ###################################################
    
    # CLOSE_SESSIONS
    # LOGIN_STRING
    # NO_PASSWORD_CONSOLE
    # QMAIL_DIR

[Linux_ _etc_login.defs]: /images/20210728/b5944102138948929c1578850ebbb1e4.png