SU(1)

名称
su - 更改用户 ID 或成为超级用户

大纲

su [options] [-] [username [ args ]]

描述

The su command is used to become another user during a login session. Invoked without a username, su defaults to becoming the superuser. The - option may be used to provide an environment similar to what the user would expect had the user logged in directly. The -c option may be used to treat the next argument as a command by most shells.

Options are recognized everywhere in the argument list. You can use the -- argument to stop option parsing. The - option is special: it is also recognized after --, but has to be placed before username.

如果合适，将提示用户输入一个密码。输入无效的密码会产生一个错误消息。所有的尝试，无论成功还是失败，都会被记录，以检测对系统的滥用。

The current environment is passed to the new shell. The value of $PATH is reset to /bin:/usr/bin for normal users, or /sbin:/bin:/usr/sbin:/usr/bin for the superuser. This may be changed with the ENV_PATH and ENV_SUPATH definitions in /etc/login.defs.

在登录 shell 中以第一个字符是“*”标注的是子系统登录。给定的主目录将被用于用户实际登录的新文件系统的根。

选项

The options which apply to the su command are:

-c, --command COMMAND
    Specify a command that will be invoked by the shell using its -c.

    The executed command will have no controlling terminal. This option cannot be used to execute interactive programs which need a controlling TTY.

-, -l, --login
    提供一个类似于用户直接登录的环境，用户可能会希望这样。

    When - is used, it must be specified before any username. For portability it is recommended to use it as last option, before any username. The other forms (-l and --login) do not have this restriction.

-s, --shell SHELL
    将使用的 shell。

    The invoked shell is chosen from (highest priority first):

        The shell specified with --shell.

        If --preserve-environment is used, the shell specified by the $SHELL environment variable.

        The shell indicated in the /etc/passwd entry for the target user.

        /bin/sh if a shell could not be found by any above method.

    If the target user has a restricted shell (i.e. the shell field of this user's entry in /etc/passwd is not listed in /etc/shells), then the --shell option or the $SHELL environment variable won't be taken into account, unless su is called by root.

-m, -p, --preserve-environment
    Preserve the current environment, except for:

    $PATH
        reset according to the /etc/login.defs options ENV_PATH or ENV_SUPATH (see below);

    $IFS
        reset to “<space><tab><newline>”, if it was set.

    If the target user has a restricted shell, this option has no effect (unless su is called by root).

    Note that the default behavior for the environment is the following:

        The $HOME, $SHELL, $USER, $LOGNAME, $PATH, and $IFS environment variables are reset.

        If --login is not used, the environment is copied, except for the variables above.

        If --login is used, the $TERM, $COLORTERM, $DISPLAY, and $XAUTHORITY environment variables are copied if they were set.

        Other environments might be set by PAM modules.

CAVEATS

This version of su has many compilation options, only some of which may be in use at any particular site.

配置文件

The following configuration variables in /etc/login.defs change the behavior of this tool:

文件

/etc/passwd
    用户账户信息。

/etc/shadow
    安全用户账户信息。

/etc/login.defs
    Shadow 密码套件配置。

退出值

On success, su returns the exit value of the command it executed.

If this command was terminated by a signal, su returns the number of this signal plus 128.

If su has to kill the command (because it was asked to terminate, and the command did not terminate in time), su returns 255.

Some exit values from su are independent from the executed command:

0
    success (--help only)

1
    System or authentication failure

126
    The requested command was not found

127
    The requested command could not be executed

参见

login(1), login.defs(5), sg(1), sh(1).