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From Ralph Bolton <Ralph.Bol...@pre-emptive.net>
Subject os-solaris/1052: Server unable to obtain correct hostname when running NIS
Date Mon, 25 Aug 1997 16:10:01 GMT

>Number:         1052
>Category:       os-solaris
>Synopsis:       Server unable to obtain correct hostname when running NIS
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    apache (Apache HTTP Project)
>State:          open
>Class:          sw-bug
>Submitter-Id:   apache
>Arrival-Date:   Mon Aug 25 09:10:01 1997
>Originator:     Ralph.Bolton@pre-emptive.net
>Organization:
apache
>Release:        Server version Apache/1.2.4.
>Environment:
SunOS aldi 5.5.1 Generic sun4c sparc SUNW,Sun_4_50
gcc version 2.7.2

Sun (Sol. 2) Running NIS with table entries in NIS hosts like "192.168.100.3 aldi"
>Description:
On a machine Sun (Sol. 2, but SunOS probably the same) name lookups are
often "nis, dns, files". Since most NIS tables don't have the full domain
name, and are something of the form:

192.168.100.3	aldi	loghost
192.168.100.4	diskserv

then the gethostbyname() lookups only return the hostname, not "hostname.domainname"
Consequently, when the server starts, it barfs saying it couldn't get the
hostname - and advises the use fo the ServerName directive.

I have reasons why I don't want to use the directive (many machines using the
same config file). As such, I'd like the server to get the hostname right
by itself.

A check of the source shows it checks to see how many dots there are in the
gethostbyname() output. If none, it quits. If there are some, it does some
clever stuff, and presumably works.

I have hacked about to get this work under Solaris 2 (should be okay under
SunOS too). I admit to this being a shamelsss hack which I haven't tested
exhastively. However, it does now get the hostname fully qualified on startup.

If anyone likes my hack, they're free to use it. "Your mileage may vary".
It won't of course work if you don't have an /etc/resolv.conf file.
>How-To-Repeat:
If running NIS, then check your NIS hosts table. If it has FQDNs in the
first column of hostnames, then change the one for your host to just "hostname".
This should also work if you're just using files.

It all hangs on the way your OS does gethostbyname(). On a Sun, it follows
/etc/nsswitch.conf (under S2). In our setup that's "NIS files". However,
SunOS it is implicit NIS only (NIS would often do the DNS on behalf of a
client though).

However, if NIS responds with just a hostname, then Apache finds no dots,
so barfs.

I guess the bottom line is make you gethostbyname() return a non-fqdn.
>Fix:
Modify util.c so that the get_local_host() function is completely replaced
by:


char *get_local_host(pool *a)
{
#ifndef MAXHOSTNAMELEN
#define MAXHOSTNAMELEN 256
#endif
    char str[MAXHOSTNAMELEN+1];
    char *server_hostname;
    struct hostent *p;

#define RALPH_MAX_LINE 200
#define RALPH_RESOLVE_FILE "/etc/resolv.conf"

	FILE *ralph_resolve;
	int ralph_exhausted=0;
	int ralph_i;
	char ralph_line[RALPH_MAX_LINE+1];
	char ralph_temp[RALPH_MAX_LINE+MAXHOSTNAMELEN];
	char *ralph_domain="domain";
	char *ralph_c;
	char ralph_orig_str[MAXHOSTNAMELEN+1];
	int ralph_go=0;



    if( gethostname( str, sizeof( str ) - 1 ) != 0 ) {
	perror( "Unable to gethostname" );
	exit(1);
    }
    str[MAXHOSTNAMELEN] = '\0';

	strncpy(ralph_orig_str,str,MAXHOSTNAMELEN);

    if((!(p=gethostbyname(str))) || (!(server_hostname = find_fqdn(a, p)))) {

	/* Ralph's additional hack... /*
	/* At this point, Apache has looked up our hostname and got */
	/* a single word, with no dots in it. Consequently, it decides */
	/* that is has not got an FQDN, so barfs. Since this is to do with */
	/* NIS, it's reasonably easy to do another check which may fix it. */
	/* All we do is to open /etc/resolv.conf and look for any */
	/* "domain" lines. All we do is try out each one with the hostname */
	/* pre-pended. If any work, then great, or, if there are no */
	/* domain lines, or if none work, then we barf as before */
	if( (ralph_resolve=fopen(RALPH_RESOLVE_FILE,"r"))!=NULL)
	{
		while(ralph_go==0)
		{
			for(ralph_i=0; ralph_i<RALPH_MAX_LINE; ralph_i++)
			{
				if((ralph_line[ralph_i]=
					getc(ralph_resolve))==EOF)
				{
					ralph_go=1;
					ralph_line[ralph_i]=0;
					ralph_i=RALPH_MAX_LINE;
				}
				if(ralph_line[ralph_i]=='\n')
				{
					ralph_line[ralph_i]=0;
					ralph_i=RALPH_MAX_LINE;
				}

				ralph_line[ralph_i]=
					tolower(ralph_line[ralph_i]);
			}
			ralph_line[ralph_i]=0;

			/* At this point, we've got a NULL terminated */
			/* string which may or may not have "domain" at */
			/* the front of it. */

			/* See if it's got "domain" at the front... */

			if(strncmp(ralph_line,ralph_domain,
				strlen(ralph_domain))==0)
			{
				/* Domain line */
				ralph_i=strlen(ralph_domain);
				ralph_c=ralph_line+ralph_i;

				/* Move pointer to start of actual domain */
				while(isspace(*(ralph_c))!=0)
				{
					ralph_c++;
				}

				sprintf(ralph_temp, "%s.%s",ralph_orig_str,
					ralph_c);
				printf("Okay, tried and got %s\n",ralph_temp);

				/* Now retest the "hostname" */

				if((!(p=gethostbyname(ralph_temp))) ||
				  (!(server_hostname = find_fqdn(a, p))))
				{
					/* Didn't work */
					;
				}
				else
				{
					/* Success! */
					fclose(ralph_resolve);
					return server_hostname;
				}

			}
		} /* of while */

		fclose(ralph_resolve);

	} /* of open file */


        fprintf(stderr,"httpd: cannot determine local host name.(%s)\n",str);
	fprintf(stderr,"Use ServerName to set it manually.\n");
	exit(1);
	}

    return server_hostname;
}


...which is obviosuly a huge hack, which relies on /etc/resolv.conf. However,
any DNS capable machine should have at least something there.

As a summary, the above code does all that Apache does normally (so it shouldn't
screw anyone already working). However, before barfing for real, it
does an additional check on /etc/resolv.conf. If it can find the file, and
it has some "domain" lines, it tests each domain until one works. It assumes
that the first one it finds which works is good (as does DNS, actually).

I never did work out how you were *supposed* to do this..
>Audit-Trail:
>Unformatted:




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