04-14-2011
Validate your input not blank, is in /etc/passwd, first, before proceeding, if bad then display, exit -- done, no deep nesting, all parts of the function point close together. A cat is not necessary to get files to stdin, < does that cheaper. One user name might be a substring of another, so the grep of who should be more qualified. date can produce the entire message using a "+%Y-%m-%d %H:%M:%S $username" sort of argument, and have a nicer format. $(xxx) is not for diplaying variables, that is ${xxx}, $(xxx) turns a command or script stdout into a string on the command line, just the opposite of echo, which turns a string on the command line into a stream on stdout. The error message does not describe the error, unnown user name.
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su(1) General Commands Manual su(1)
Name
su - substitute a user ID
Syntax
su [username]
su - [username]
su -f [username]
Description
The command requests the password of the specified username. If the correct password is given, changes to that username without changing
the current directory. The user environment is unchanged except for HOME and SHELL which are taken from the password file entry for user-
name. The shell that is run is also taken from the password file entry for username. The new user ID stays in force until the shell
exits.
If no username is specified, `root' is assumed. To remind the superuser of his responsibilities, the shell substitutes `#' for its usual
prompt.
Options
-f Prevents from executing the .cshrc file, making start up faster.
- Simulates a full login.
Diagnostics
Sorry
An invalid password was supplied for the specified username.
Unknown login: username
The specified username was not found in the passwd database.
No directory
The home directory for the username is not accessible at this time (only with ``-'' argument).
No shell
The shell specified in the passwd database entry for username could not be executed.
Kerberos initialization failure
Consult your system administrator.
If enhanced security features are enabled the following error messages are also possible:
Requires secure terminal
Attempt to su to UID 0 on a line that is not marked secure in
User's password has expired
Access is denied because the password for username is expired.
This account is disabled
Access is denied because the auth entry corresponding to username is marked disabled.
Files
Log file of anyone who became
root, with a date mark.
See Also
csh(1), sh(1), passwd(5yp), environ(7), edauth(8)
Security Guide for Administrators
Security Guide for Users
su(1)