/etc/login.defs文件
配置文件/etc/login.defs用来定义创建用户账号时的默认设置
比如指定用户UID和GID的范围、账号的过期时间和是否需要创建用户家目录等
查看 /etc/login.defs 文件
[root@iZ8vb9nmgwljcf9m2wxaekZ ~]# cat /etc/login.defs # # Please note that the parameters in this configuration file control the # behavior of the tools from the shadow-utils component. None of these # tools uses the PAM mechanism, and the utilities that use PAM (such as the # passwd command) should therefore be configured elsewhere. Refer to # /etc/pam.d/system-auth for more information. # # *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 1000 UID_MAX 60000 # System accounts SYS_UID_MIN 201 SYS_UID_MAX 999 # # Min/max values for automatic gid selection in groupadd # GID_MIN 1000 GID_MAX 60000 # System accounts SYS_GID_MIN 201 SYS_GID_MAX 999 # # 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 overridden with the -m flag on # useradd command line. # CREATE_HOME yes # The permission mask is initialized to this value. If not specified, # the permission mask will be initialized to 022. UMASK 077 # This enables userdel to remove user groups if no members exist. # USERGROUPS_ENAB yes # Use SHA512 to encrypt password. ENCRYPT_METHOD SHA512 # # Please note that the parameters in this configuration file control the # behavior of the tools from the shadow-utils component. None of these # tools uses the PAM mechanism, and the utilities that use PAM (such as the # passwd command) should therefore be configured elsewhere. Refer to # /etc/pam.d/system-auth for more information. # # *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 1000 UID_MAX 60000 # System accounts SYS_UID_MIN 201 SYS_UID_MAX 999 # # Min/max values for automatic gid selection in groupadd # GID_MIN 1000 GID_MAX 60000 # System accounts SYS_GID_MIN 201 SYS_GID_MAX 999 # # 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 overridden with the -m flag on # useradd command line. # CREATE_HOME yes # The permission mask is initialized to this value. If not specified, # the permission mask will be initialized to 022. UMASK 077 # This enables userdel to remove user groups if no members exist. # USERGROUPS_ENAB yes # Use SHA512 to encrypt password. ENCRYPT_METHOD SHA512
参数说明：
USERGROUPS_ENAB yes ： 这行指定的是使用命令 userdel 删除用户时，是否删除用户的初始组，默认是删除。
ENCRYPT_METHOD SHA512：指定 Linux 用户的密码使用 SHA512 散列模式加密，这是新的密码加密模式，原先的 Linux只能用 DES 或 MD5 方式加密
注意：修改该文件中的设置，只针对新创建的用户有效。
例如，限制用户的密码有效期（最大天数）为30天，可以将“PASS_MAX_DAYS”的值设为30，
那么在修改完该配置文件之后，所有新创建用户的密码有效期将是30天。
/etc/skel目录
在创建完用户之后，Linux系统会自动在用户的家目录中产生一些默认的文件，这些文件大多是隐藏的
实例：查看 user2用户家目录默认文件
[root@iZ8vb9nmgwljcf9m2wxaekZ ~]# ls -a /home/user2 . .. .bash_logout .bash_profile .bashrc
这些文件可以用于设置用户的运行环境，或者用于设置用户登录或退出时自动执行某些操作。
例如“.bash_profile”和“.bashrc”文件用于设置用户登录时自动执行某些操作，
“.bash_logout”文件则用于设置用户退出系统时自动执行某些操作
/etc/skel目录为所有的这些默认文件提供了模板，如果在/etc/skel目录中建立目录或放入文件，
那么所有新创建的用户的家目录中就会有这些目录及文件。
如果修改该目录中的用户配置文件、登录脚本等内容，那么新建用户的用户配置文件、登录脚本也会采用修改后的内容。