SU(1) SU(1) su - su [] [-] [user|UID [argument...]] su . su root . . su HOME SHELL ( USER LOGNAME root). --login ( -) . su PAM . su wheel PAM. su ( root) set-user-ID runuser(1) PAM . PAM setpriv(1). su PAM (pam_getenvlist(3)) . --login --preserve-environment PAM. 2.38 su RLIMIT_NICE RLIMIT_RTPRIO RLIMIT_FSIZE RLIMIT_AS RLIMIT_NOFILE. -c --command command -c. setsid(2). --session-command . -f --fast -f . -g --group . root . -G --supp-group . (root) . --group. - -l --login . systemd(1) . su ( PAM) . systemd-run(1) machinectl(1) . su : o clear all the environment variables except TERM, COLORTERM, NO_COLOR and variables specified by --whitelist-environment o initialize the environment variables HOME, SHELL, USER, LOGNAME, and PATH o change to the target user's home directory o set argv[0] of the shell to '-' in order to make the shell a login shell -m -p --preserve-environment HOME SHELL USER LOGNAME. --login. -P --pty . . TIOCSTI . ( su --pty - user -c application &). su ( ). . (: echo "date" | su --pty) ECHO . -s --shell . ( /etc/shells) --shell SHELL root. : o --shell o SHELL --preserve-environment o passwd o /bin/sh --session-command= -c . ( .) TIOCSTI . -T --no-pty --pty -P. TIOCSTI . -w --whitelist-environment --login. HOME SHELL USER LOGNAME PATH. -h --help . -V --version . SIGINT SIGQUIT SIGTERM su . SIGTERM SIGKILL. su /etc/default/su /etc/login.defs. su: FAIL_DELAY (number) . . ENV_PATH (string) PATH . /usr/local/bin:/bin:/usr/bin. ENV_ROOTPATH (string), ENV_SUPATH ( ) PATH root. ENV_SUPATH. /usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin. ALWAYS_SET_PATH () yes --login --preserve-environment su PATH. PATH /bin /sbin /usr --login PAM ( (8)pam_env). su . su + 128. su : 1 126 127 /etc/pam.d/su PAM /etc/pam.d/su-l PAM --login /etc/default/su logindef /etc/login.defs logindef su ioctl TIOCSTI/TIOCLINUX. : su -c setsid(2) . su --pty -P. su btmp lastlog . su PAM. pam_lastlog(8) pam_lastlog(8) lastlog . : session required pam_lastlog.so nowtmp su su coreutils David MacKenzie. util-linux Karel Zak. setpriv(1) login.defs(5) shells(5) pam(8) runuser(1) . su util-linux . util-linux 2.42.1 2026-05-18 SU(1)