diff --git a/mysql-test/r/variables.result b/mysql-test/r/variables.result
index c3d7d5ac4eb..60010183d32 100644
--- a/mysql-test/r/variables.result
+++ b/mysql-test/r/variables.result
@@ -752,6 +752,14 @@ select @@&;
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '&' at line 1
 select @@@;
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '@' at line 1
+select @@hostname;
+@@hostname
+#
+set @@hostname= "anothername";
+ERROR HY000: Variable 'hostname' is a read only variable
+show variables like 'hostname';
+Variable_name	Value
+hostname	#
 End of 5.0 tests
 set global binlog_cache_size         =@my_binlog_cache_size;
 set global connect_timeout           =@my_connect_timeout;
diff --git a/mysql-test/t/variables.test b/mysql-test/t/variables.test
index 5edb8fb754b..697e55945ef 100644
--- a/mysql-test/t/variables.test
+++ b/mysql-test/t/variables.test
@@ -639,6 +639,17 @@ select @@&;
 --error ER_PARSE_ERROR
 select @@@;
 
+#
+# Bug#20166 mysql-test-run.pl does not test system privilege tables creation
+#
+# Don't actually output, since it depends on the system
+--replace_column 1 #
+select @@hostname;
+--error 1238
+set @@hostname= "anothername";
+--replace_column 2 #
+show variables like 'hostname';
+
 --echo End of 5.0 tests
 
 # This is at the very after the versioned tests, since it involves doing
diff --git a/sql/log.cc b/sql/log.cc
index 1961a5b6f88..9b47de05c86 100644
--- a/sql/log.cc
+++ b/sql/log.cc
@@ -452,7 +452,7 @@ const char *MYSQL_LOG::generate_name(const char *log_name,
       TODO: The following should be using fn_format();  We just need to
       first change fn_format() to cut the file name if it's too long.
     */
-    strmake(buff,glob_hostname,FN_REFLEN-5);
+    strmake(buff, pidfile_name,FN_REFLEN-5);
     strmov(fn_ext(buff),suffix);
     return (const char *)buff;
   }
diff --git a/sql/mysqld.cc b/sql/mysqld.cc
index 2842d2e8b2f..1f65b50b98d 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -2636,9 +2636,15 @@ static int init_common_variables(const char *conf_file_name, int argc,
   mysql_slow_log.init_pthread_objects();
   mysql_bin_log.init_pthread_objects();
 
-  if (gethostname(glob_hostname,sizeof(glob_hostname)-4) < 0)
-    strmov(glob_hostname,"mysql");
-  strmake(pidfile_name, glob_hostname, sizeof(pidfile_name)-5);
+  if (gethostname(glob_hostname,sizeof(glob_hostname)) < 0)
+  {
+    strmake(glob_hostname, STRING_WITH_LEN("localhost"));
+    sql_print_warning("gethostname failed, using '%s' as hostname",
+                      glob_hostname);
+    strmake(pidfile_name, STRING_WITH_LEN("mysql"));
+  }
+  else
+    strmake(pidfile_name, glob_hostname, sizeof(pidfile_name)-5);
   strmov(fn_ext(pidfile_name),".pid");		// Add proper extension
 
   load_defaults(conf_file_name, groups, &argc, &argv);
@@ -3087,7 +3093,7 @@ server.");
   if (opt_error_log)
   {
     if (!log_error_file_ptr[0])
-      fn_format(log_error_file, glob_hostname, mysql_data_home, ".err",
+      fn_format(log_error_file, pidfile_name, mysql_data_home, ".err",
                 MY_REPLACE_EXT); /* replace '.<domain>' by '.err', bug#4997 */
     else
       fn_format(log_error_file, log_error_file_ptr, mysql_data_home, ".err",
diff --git a/sql/set_var.cc b/sql/set_var.cc
index 29917f2f83c..b3a9305132a 100644
--- a/sql/set_var.cc
+++ b/sql/set_var.cc
@@ -590,6 +590,10 @@ sys_var_readonly                sys_have_innodb("have_innodb", OPT_GLOBAL,
 /* Global read-only variable describing server license */
 sys_var_const_str		sys_license("license", STRINGIFY_ARG(LICENSE));
 
+/* Global read-only variable containing hostname */
+sys_var_const_str		sys_hostname("hostname", glob_hostname);
+
+
 
 /*
   List of all variables for initialisation and storage in hash
@@ -642,6 +646,7 @@ sys_var *sys_variables[]=
   &sys_foreign_key_checks,
   &sys_group_concat_max_len,
   &sys_have_innodb,
+  &sys_hostname,
   &sys_identity,
   &sys_init_connect,
   &sys_init_slave,
@@ -874,6 +879,7 @@ struct show_var_st init_vars[]= {
   {"have_raid",		      (char*) &have_raid,		    SHOW_HAVE},
   {"have_rtree_keys",         (char*) &have_rtree_keys,             SHOW_HAVE},
   {"have_symlink",            (char*) &have_symlink,                SHOW_HAVE},
+  {sys_hostname.name,         (char*) &sys_hostname,                SHOW_SYS},
   {"init_connect",            (char*) &sys_init_connect,            SHOW_SYS},
   {"init_file",               (char*) &opt_init_file,               SHOW_CHAR_PTR},
   {"init_slave",              (char*) &sys_init_slave,              SHOW_SYS},