Not able to do "su -" . getting error "su: user - does not exist " !

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux (All Versions)

Issue

  • Not able to do "su -" . getting error "su: user - does not exist " !
[testsys] /home/alpha> su -
su: user - does not exist
  • If execute 'su' the able to login as 'root'

Resolution

  • Remove alias, or use "su".
  • Alias is defined in .bashrc file of user home directory.
# .bashrc

# User specific aliases and functions

alias rm='rm -i'
alias cp='cp -i'
alias mv='mv -i'
alias su='su -'                      ------------------here
# Source global definitions
if [ -f /etc/bashrc ]; then
        . /etc/bashrc
fi

Root Cause

  • An alias was in place that replaced "su" with "su -". The effective command being run was "su - -", causing the syntax error.

Diagnostic Steps

  • Running an strace displayed the root user logging in correctly. Aliases would not be in effect during the strace.

  • su always considers the last (or singular) argument presented to it is the intended login name, except for when issuing a "su -" by itsself:

  if (optind < argc && STREQ (argv[optind], "-"))
    {
      simulate_login = true;
      ++optind;
    }
  if (optind < argc)
    new_user = argv[optind++];          <--- optind being one less than argc, optind++ will be the last arg 

  pw = getpwnam (new_user);
  if (! (pw && pw->pw_name && pw->pw_name[0] && pw->pw_dir && pw->pw_dir[0]
     && pw->pw_passwd))                                                      <-- full check for valid user
    error (EXIT_FAIL, 0, _("user %s does not exist"), new_user);
  • Only issuing an incorrect "su options -" would cause the program to try to look up "-" as a user. An alias must be in place.

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