su 命令

帮助信息

su --help

$ su --help
Usage: su [options] [LOGIN]Options:-c, --command COMMAND         pass COMMAND to the invoked shell-h, --help                    display this help message and exit-, -l, --login                make the shell a login shell-m, -p,--preserve-environment        do not reset environment variables, andkeep the same shell-s, --shell SHELL             use SHELL instead of the default in passwd

man su

$ man su
SU(1)                            User Commands                           SU(1)NAMEsu - change user ID or become superuserSYNOPSISsu [options] [username]DESCRIPTIONThe su command is used to become another user during a login session.Invoked without a username, su defaults to becoming the superuser. Theoptional argument - may be used to provide an environment similar towhat the user would expect had the user logged in directly.Additional arguments may be provided after the username, in which casethey are supplied to the user's login shell. In particular, an argumentof -c will cause the next argument to be treated as a command by mostcommand interpreters. The command will be executed by the shellspecified in /etc/passwd for the target user.You can use the -- argument to separate su options from the argumentssupplied to the shell.The user will be prompted for a password, if appropriate. Invalidpasswords will produce an error message. All attempts, both valid andinvalid, are logged to detect abuse of the system.The current environment is passed to the new shell. The value of $PATHis reset to /bin:/usr/bin for normal users, or/sbin:/bin:/usr/sbin:/usr/bin for the superuser. This may be changedwith the ENV_PATH and ENV_SUPATH definitions in /etc/login.defs.A subsystem login is indicated by the presence of a "*" as the firstcharacter of the login shell. The given home directory will be used asthe root of a new file system which the user is actually logged into.OPTIONSThe options which apply to the su command are:-c, --command COMMANDSpecify a command that will be invoked by the shell using its -c.The executed command will have no controlling terminal. This optioncannot be used to execute interactive programs which need acontrolling TTY.-, -l, --loginProvide an environment similar to what the user would expect hadthe user logged in directly.When - is used, it must be specified before any username. Forportability it is recommended to use it as last option, before anyusername. The other forms (-l and --login) do not have thisrestriction.-s, --shell SHELLThe shell that will be invoked.The invoked shell is chosen from (highest priority first):The shell specified with --shell.If --preserve-environment is used, the shell specified by the$SHELL environment variable.The shell indicated in the /etc/passwd entry for the targetuser./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 ofthis user's entry in /etc/passwd is not listed in /etc/shells),then the --shell option or the $SHELL environment variable won't betaken into account, unless su is called by root.-m, -p, --preserve-environmentPreserve the current environment, except for:$PATHreset according to the /etc/login.defs options ENV_PATH orENV_SUPATH (see below);$IFSreset to “<space><tab><newline>”, if it was set.If the target user has a restricted shell, this option has noeffect (unless su is called by root).Note that the default behavior for the environment is thefollowing:The $HOME, $SHELL, $USER, $LOGNAME, $PATH, and $IFS environmentvariables are reset.If --login is not used, the environment is copied, except forthe 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.CAVEATSThis version of su has many compilation options, only some of which maybe in use at any particular site.CONFIGURATIONThe following configuration variables in /etc/login.defs change thebehavior of this tool:CONSOLE_GROUPS (string)List of groups to add to the user's supplementary groups set whenlogging in on the console (as determined by the CONSOLE setting).Default is none.Use with caution - it is possible for users to gain permanentaccess to these groups, even when not logged in on the console.DEFAULT_HOME (boolean)Indicate if login is allowed if we can't cd to the home directory.Default is no.If set to yes, the user will login in the root (/) directory if itis not possible to cd to her home directory.ENV_PATH (string)If set, it will be used to define the PATH environment variablewhen a regular user login. The value is a colon separated list ofpaths (for example /bin:/usr/bin) and can be preceded by PATH=. Thedefault value is PATH=/bin:/usr/bin.ENV_SUPATH (string)If set, it will be used to define the PATH environment variablewhen the superuser login. The value is a colon separated list ofpaths (for example /sbin:/bin:/usr/sbin:/usr/bin) and can bepreceded by PATH=. The default value isPATH=/sbin:/bin:/usr/sbin:/usr/bin.SULOG_FILE (string)If defined, all su activity is logged to this file.SU_NAME (string)If defined, the command name to display when running "su -". Forexample, if this is defined as "su" then a "ps" will display thecommand is "-su". If not defined, then "ps" would display the nameof the shell actually being run, e.g. something like "-sh".SYSLOG_SU_ENAB (boolean)Enable "syslog" logging of su activity - in addition to sulog filelogging.FILES/etc/passwdUser account information./etc/shadowSecure user account information./etc/login.defsShadow password suite configuration.EXIT VALUESOn success, su returns the exit value of the command it executed.If this command was terminated by a signal, su returns the number ofthis signal plus 128.If su has to kill the command (because it was asked to terminate, andthe command did not terminate in time), su returns 255.Some exit values from su are independent from the executed command:0success (--help only)1System or authentication failure126The requested command was not found127The requested command could not be executedSEE ALSOlogin(1), login.defs(5), sg(1), sh(1).shadow-utils 4.5                  08/21/2019                             SU(1)

示例

切换用户

mk@mk-Lenovo-Y430P:~$ whoami // 当前用户
mk
mk@mk-Lenovo-Y430P:~$ pwd // 当前工作目录
/home/mk
mk@mk-Lenovo-Y430P:~$ su root // 切换到 root 用户
Password:
root@mk-Lenovo-Y430P:/home/mk# whoami
root
root@mk-Lenovo-Y430P:/home/mk# pwd
/home/mk

当只切换用户而不改变环境变量时，执行某些命令将受限。例如，查看 Java 的版本信息：

root@mk-Lenovo-Y430P:/home/mk# java -versionCommand 'java' not found, but can be installed with:apt install default-jre
apt install openjdk-11-jre-headless
apt install openjdk-8-jre-headless

切换用户，并改变环境变量

mk@mk-Lenovo-Y430P:~$ whoami
mk
mk@mk-Lenovo-Y430P:~$ pwd
/home/mk
mk@mk-Lenovo-Y430P:~$ su --login root
Password:
root@mk-Lenovo-Y430P:~# whoami
root
root@mk-Lenovo-Y430P:~# pwd
/root

在这种情况下，能正常执行 java -version 命令：

root@mk-Lenovo-Y430P:~# java -version
java version "1.8.0_241"
Java(TM) SE Runtime Environment (build 1.8.0_241-b07)
Java HotSpot(TM) 64-Bit Server VM (build 25.241-b07, mixed mode)

参考

Linux su 命令

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Linux su 命令

文章目录

su 命令

帮助信息

su --help

man su

示例

切换用户

切换用户，并改变环境变量

参考

Linux su 命令相关推荐

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