[root@vps152 pga]# su postgres -c pg_ctl restart
bash: /root/.bashrc: Permission denied
pg_ctl: no operation mode specified
Try 'pg_ctl --help' for more information.
[root@vps152 pga]# su postgres -c pg_ctl --help
Usage: su [OPTION]... [-] [USER [ARG]...]
Change the effective user id and group id to that of USER.

  -, -l, --login               make the shell a login shell
  -c, --commmand=COMMAND       pass a single COMMAND to the shell with -c
  -f, --fast                   pass -f to the shell (for csh or tcsh)
  -m, --preserve-environment   do not reset environment variables
  -p                           same as -m
  -s, --shell=SHELL            run SHELL if /etc/shells allows it
      --help     display this help and exit
      --version  output version information and exit

A mere - implies -l.   If USER not given, assume root.

Report bugs to <bug-coreutils@gnu.org>.