# useradd -M nmbd
# chmod 775 /var/cache/samba
# chgrp nmbd /var/cache/samba
# chown nmbd:nmbd /var/cache/samba/messages.tdb
# nmbd -D -u nmbd

(look out for other permission errors)

--- samba-2.2.3a/source/Makefile.in.bak	2002-04-07 02:52:55.000000000 +0300
+++ samba-2.2.3a/source/Makefile.in	2002-04-07 16:36:35.000000000 +0300
@@ -492,7 +492,7 @@ bin/smbd: $(SMBD_OBJ) bin/.dummy
 
 bin/nmbd: $(NMBD_OBJ) bin/.dummy
 	@echo Linking $@
-	@$(CC) $(FLAGS) -o $@ $(NMBD_OBJ) $(LDFLAGS) $(LIBS)
+	@$(CC) $(FLAGS) -o $@ $(NMBD_OBJ) $(LDFLAGS) $(LIBS) -lcap
 
 bin/swat: $(SWAT_OBJ) bin/.dummy
 	@echo Linking $@
--- samba-2.2.3a/source/nmbd/nmbd.c.bak	2002-04-07 02:52:55.000000000 +0300
+++ samba-2.2.3a/source/nmbd/nmbd.c	2002-04-07 17:07:30.000000000 +0300
@@ -25,6 +25,8 @@
 
 */
 
+#include <sys/prctl.h>
+
 #include "includes.h"
 
 pstring servicesf = CONFIGFILE;
@@ -34,6 +36,7 @@ int ClientDGRAM     = -1;
 int global_nmb_port = -1;
 
 static pstring host_file;
+static pstring nmbd_user;
 extern pstring global_myname;
 extern fstring global_myworkgroup;
 extern char **my_netbios_names;
@@ -635,7 +638,7 @@ static void usage(char *pname)
 {
 
   printf( "Usage: %s [-DaiohV] [-H lmhosts file] [-d debuglevel] [-l log basename]\n", pname );
-  printf( "       [-n name] [-p port] [-s configuration file]\n" );
+  printf( "       [-n name] [-p port] [-s configuration file] [-u user]\n" );
   printf( "\t-D                    Become a daemon (default)\n" );
   printf( "\t-a                    Append to log file (default)\n" );
   printf( "\t-i                    Run interactive (not a daemon)\n" );
@@ -648,10 +651,66 @@ static void usage(char *pname)
   printf( "\t-n netbiosname.       Primary netbios name\n" );
   printf( "\t-p port               Listen on the specified port\n" );
   printf( "\t-s configuration file Configuration file name\n" );
+  printf( "\t-u user               Run as this uid/gid (default: root)" );
   printf( "\n");
 } /* usage */
 
+/************************************************************************
+ switch user/group of nmbd process, keep CAP_NET_BIND_SERVICE capability
+ by Sami Farin <safari@iki.fi>
+************************************************************************/
+
+static void nmbd_droproot(void);
+static void nmbd_droproot(void)
+{
+  struct passwd* pwd;
+  uid_t nmbd_uid;
+  gid_t nmbd_gids[1];
+  cap_t nmbd_caps;
+
+  if( (pwd = getpwnam( nmbd_user )) == NULL) {
+    DEBUG( 0, ( "getpwnam failed for \"%s\"\n", nmbd_user ) );
+    exit(1);
+  }
+
+  nmbd_uid = pwd->pw_uid;
+  nmbd_gids[0] = pwd->pw_gid;
+
+  /* keep capabilities on setuid() away from uid 0 */
+  if( prctl( PR_SET_KEEPCAPS, 1) != 0 ) {
+    DEBUG( 0, ( "prctl failed\n" ) );
+    exit(1);
+  }
+
+  if( setgroups( 1, nmbd_gids ) == -1 ) {
+    DEBUG( 0, ( "setgroups failed\n" ) );
+    exit(1);
+  }
+
+  if( (setegid(nmbd_gids[0]) == -1) || (seteuid(nmbd_uid) == -1) ) {
+    DEBUG( 0, ( "setegid and/or seteuid failed\n" ) );
+	exit(1);
+  }
+
+  if( (nmbd_caps = cap_from_text( "cap_net_bind_service=epi" ) ) == NULL) {
+	DEBUG( 0, ( "cap_from_text failed\n" ) );
+	exit(1);
+  }
+
+  if( cap_set_proc( nmbd_caps ) == -1) {
+	DEBUG( 0, ( "cap_set_proc failed\n" ) );
+	exit(1);
+  }
+
+  (void)cap_free( nmbd_caps );
 
+  if( (setregid( nmbd_gids[0], nmbd_gids[0] ) == -1) ||
+	  (setreuid( nmbd_uid, nmbd_uid ) == -1) ) {
+    DEBUG( 0, ( "setregid and/or setreuid failed\n") );
+	exit(1);
+  }
+}
+  
 /**************************************************************************** **
  Main program.
  **************************************************************************** */
@@ -669,6 +728,7 @@ static void usage(char *pname)
 
   global_nmb_port = NMB_PORT;
   *host_file = 0;
+  *nmbd_user = 0;
   global_in_nmbd = True;
 
   StartupTime = time(NULL);
@@ -686,6 +746,8 @@ static void usage(char *pname)
   pstrcpy( host_file, LMHOSTSFILE );
 #endif
 
+  pstrcpy( nmbd_user, "root" ); /* backwards compatibility */
+
   /* this is for people who can't start the program correctly */
   while (argc > 1 && (*argv[1] != '-'))
   {
@@ -715,13 +777,16 @@ static void usage(char *pname)
 #endif
 
   while( EOF != 
-         (opt = getopt( argc, argv, "Vaos:T:I:C:bAB:N:Rn:l:d:Dip:hSH:G:f:" )) )
+         (opt = getopt( argc, argv, "Vaos:T:I:C:bAB:N:Rn:l:d:Dip:hSH:G:f:u:" )) )
     {
       switch (opt)
         {
         case 's':
           pstrcpy(servicesf,optarg);
-          break;          
+          break;
+        case 'u':
+          pstrcpy(nmbd_user,optarg);
+          break;
         case 'N':
         case 'B':
         case 'I':
@@ -844,6 +909,7 @@ static void usage(char *pname)
   }
 
   pidfile_create("nmbd");
+  nmbd_droproot();
   message_init();
   message_register(MSG_FORCE_ELECTION, nmbd_message_election);