su Command Details: Signals, Configuration, Exit Status, and Files

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. -h, --help Display help text and exit. -V, --version Print version 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 found FILES /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 file NOTES 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 nowtmp HISTORY 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 https://github.com/util-linux/util-linux/issues. AVAILABILITY The su command is part of the util-linux package which can be downloaded from Linux Kernel Archive <https://www.kernel.org/pub/linux/utils/util-linux/>. util-linux 2.39.1 2023‐06‐14 SU(1)

This section outlines how `su` handles signals, reads configuration files like `/etc/default/su` and `/etc/login.defs` (including settings for `FAIL_DELAY`, `ENV_PATH`, and `ALWAYS_SET_PATH`), and reports exit statuses. It lists relevant files like PAM configuration files and logindef config files. It also details the logging behavior of failed login attempts and provides historical context, related commands, bug reporting information, and availability details for the `su` command.