su指令帮助手册

su指令是Linux从业人员必备的核心指令之一，如下为su指令的帮助手册。

SU(1)                                                User Commands                                               SU(1)NAME       su - run a command with substitute user and group IDSYNOPSIS       su [options] [-] [user [argument...]]DESCRIPTION       su allows commands to be run with a substitute user and group ID.       When called with no user specified, su defaults to running an interactive shell as root. When user is       specified, additional arguments can be supplied, in which case they are passed to the shell.       For backward compatibility, su defaults to not change the current directory and to only set the environment       variables HOME and SHELL (plus USER and LOGNAME if the target user is not root). It is recommended to always       use the --login option (instead of its shortcut -) to avoid side effects caused by mixing environments.       This version of su uses PAM for authentication, account and session management. Some configuration options       found in other su implementations, such as support for a wheel group, have to be configured via PAM.       su is mostly designed for unprivileged users, the recommended solution for privileged users (e.g., scripts       executed by root) is to use non-set-user-ID command runuser(1) that does not require authentication and       provides separate PAM configuration. If the PAM session is not required at all then the recommended solution is       to use command setpriv(1).       Note that su in all cases uses PAM (pam_getenvlist(3)) to do the final environment modification. Command-line       options such as --login and --preserve-environment affect the environment before it is modified by PAM.OPTIONS       -c, --command=command           Pass command to the shell with the -c option.       -f, --fast           Pass -f to the shell, which may or may not be useful, depending on the shell.       -g, --group=group           Specify the primary group. This option is available to the root user only.       -G, --supp-group=group           Specify a supplementary group. This option is available to the root user only. The first specified           supplementary group is also used as a primary group if the option --group is not specified.       -, -l, --login           Start the shell as a login shell with an environment similar to a real login:           •   clears all the environment variables except TERM and variables specified by --whitelist-environment           •   initializes the environment variables HOME, SHELL, USER, LOGNAME, and PATH           •   changes to the target user’s home directory           •   sets argv[0] of the shell to '-' in order to make the shell a login shell       -m, -p, --preserve-environment           Preserve the entire environment, i.e., do not set HOME, SHELL, USER or LOGNAME. This option is ignored if           the option --login is specified.       -P, --pty           Create a pseudo-terminal for the session. The independent terminal provides better security as the user           does not share a terminal with the original session. This can be used to avoid TIOCSTI ioctl terminal           injection and other security attacks against terminal file descriptors. The entire session can also be           moved to the background (e.g., "su --pty - username -c application &"). If the pseudo-terminal is enabled,           then su works as a proxy between the sessions (copy stdin and stdout).           This feature is mostly designed for interactive sessions. If the standard input is not a terminal, but for           example a pipe (e.g., echo "date" | su --pty), then the ECHO flag for the pseudo-terminal is disabled to           avoid messy output.       -s, --shell=shell           Run the specified shell instead of the default. The shell to run is selected according to the following           rules, in order:           •   the shell specified with --shell           •   the shell specified in the environment variable SHELL, if the --preserve-environment option is used           •   the shell listed in the passwd entry of the target user           •   /bin/sh       If the target user has a restricted shell (i.e., not listed in /etc/shells), the --shell option and the SHELL       environment variables are ignored unless the calling user is root.       --session-command=command           Same as -c, but do not create a new session. (Discouraged.)       -w, --whitelist-environment=list           Don’t reset the environment variables specified in the comma-separated list when clearing the environment           for --login. The whitelist is ignored for the environment variables HOME, SHELL, USER, LOGNAME, and PATH.       -V, --version           Display version information and exit.       -h, --help           Display help text and exit.SIGNALS       Upon receiving either SIGINT, SIGQUIT or SIGTERM, su terminates its child and afterwards terminates itself with       the received signal. The child is terminated by SIGTERM, after unsuccessful attempt and 2 seconds of delay the       child is killed by SIGKILL.CONFIG FILES       su reads the /etc/default/su and /etc/login.defs configuration files. The following configuration items are       relevant for su:       FAIL_DELAY (number)           Delay in seconds in case of an authentication failure. The number must be a non-negative integer.       ENV_PATH (string)           Defines the PATH environment variable for a regular user. The default value is           /usr/local/bin:/bin:/usr/bin.       ENV_ROOTPATH (string), ENV_SUPATH (string)           Defines the PATH environment variable for root. ENV_SUPATH takes precedence. The default value is           /usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin.       ALWAYS_SET_PATH (boolean)           If set to yes and --login and --preserve-environment were not specified su initializes PATH.           The environment variable PATH may be different on systems where /bin and /sbin are merged into /usr; this           variable is also affected by the --login command-line option and the PAM system setting (e.g., pam_env(8)).EXIT STATUS       su normally returns the exit status of the command it executed. If the command was killed by a signal, su       returns the number of the signal plus 128.       Exit status generated by su itself:       1           Generic error before executing the requested command       126           The requested command could not be executed       127           The requested command was not foundFILES       /etc/pam.d/su           default PAM configuration file       /etc/pam.d/su-l           PAM configuration file if --login is specified       /etc/default/su           command specific logindef config file       /etc/login.defs           global logindef config fileNOTES       For security reasons, su always logs failed log-in attempts to the btmp file, but it does not write to the       lastlog file at all. This solution can be used to control su behavior by PAM configuration. If you want to use       the pam_lastlog(8) module to print warning message about failed log-in attempts then pam_lastlog(8) has to be       configured to update the lastlog file as well. For example by:          session required pam_lastlog.so nowtmpHISTORY       This su command was derived from coreutils' su, which was based on an implementation by David MacKenzie. The       util-linux version has been refactored by Karel Zak.SEE ALSO       setpriv(1), login.defs(5), shells(5), pam(8), runuser(1)REPORTING BUGS       For bug reports, use the issue tracker at        The su command is part of the util-linux package which can be downloaded from Linux Kernel Archive       <;.util-linux 2.37.2                                     2021-06-02                                                 SU(1)