Fix to sidestep nonexistent/nonexecutable shell. 4.2BSD.

[Hans Albertsson]

[Wasn't that tasty?]
	If the desired shell ( as entered in /etc/passwd ) doesn't
	exist, or isn't executable, login simply quits.
	If this happens to be the shell used by root, you're in deep
	trouble.
	The following fix to login.c tries for the standard shells
	in turn, testing each on the way, first csh, then sh.
	Possibly applies to other unices, but found on 4.2BSD.
	
	In response to all disbelieving cries:
		YES it DID happen to me...
		My own fault, too.

Here are the rcsdiffs.
Apply to /usr/src/bin/login.c
------------------------------------------------------------------------
RCS file: login.c,v
retrieving revision 1.1
retrieving revision 1.5
diff  -r1.1 -r1.5
65a66
> extern	char *sys_errlist[];
155c156,157
< 		if (!strcmp(pwd->pw_shell, "/bin/csh")) {
---
> 		if (!strcmp(pwd->pw_shell, "/bin/csh") ||
> 		    !strcmp(pwd->pw_shell, "/bin/tcsh") ) {
201a204,222
> /*
>  * See if the suggested shell is executable. Otherwise use a default
>  * shell. Hoping that "sh" at least isn't in trouble...
>  *
>  */
> #define X_OK 1
> 		if (access( pwd->pw_shell, X_OK ) == -1 ) {
> 			printf("Desired shell(%s) unavailable.\n",
> 							pwd->pw_shell);
> 			printf("%s: %s\n",pwd->pw_shell,sys_errlist[errno]);
> 			pwd->pw_shell = "/bin/csh";
> 			if (access( pwd->pw_shell, X_OK ) == -1 ) {
> 				pwd->pw_shell = "/bin/sh";
> 				if (access( pwd->pw_shell, X_OK ) == -1 ) {
> 				     printf("Cannot find usable shell. Find a guru.");
> 				}
> 			}
> 			printf("Using %s instead.\n",pwd->pw_shell);
> 		}
------------------------------------------------------------------------
-- 
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			Hans Albertsson, 
			TeleLOGIC AB
			Box 1001,
			S-14901 Nynashamn,
			SWEDEN