diff --git a/mysql-test/r/variables.result b/mysql-test/r/variables.result
index ec4c7c9b2aa..cfe2f04c94d 100644
--- a/mysql-test/r/variables.result
+++ b/mysql-test/r/variables.result
@@ -903,6 +903,14 @@ 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 4f91b75ced1..16fcae380b2 100644
--- a/mysql-test/t/variables.test
+++ b/mysql-test/t/variables.test
@@ -689,6 +689,17 @@ 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 5e9ebfcb902..72baecaf7a6 100644
--- a/sql/log.cc
+++ b/sql/log.cc
@@ -2297,7 +2297,7 @@ 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 cbba3a93458..4ffdc8a75f6 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -2677,9 +2677,15 @@ static int init_common_variables(const char *conf_file_name, int argc,
   */
   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
 
   /*
diff --git a/sql/set_var.cc b/sql/set_var.cc
index 8a31cdf32ce..1e41618e08d 100644
--- a/sql/set_var.cc
+++ b/sql/set_var.cc
@@ -655,6 +655,10 @@ sys_var_thd_time_zone            sys_time_zone("time_zone");
 
 /* Read only variables */
 
+/* Global read-only variable containing hostname */
+sys_var_const_str		sys_hostname("hostname", glob_hostname);
+
+
 sys_var_have_variable sys_have_compress("have_compress", &have_compress);
 sys_var_have_variable sys_have_crypt("have_crypt", &have_crypt);
 sys_var_have_variable sys_have_csv_db("have_csv", &have_csv_db);
@@ -779,6 +783,7 @@ SHOW_VAR init_vars[]= {
   {sys_var_general_log.name, (char*) &opt_log,                      SHOW_MY_BOOL},
   {sys_var_general_log_path.name, (char*) &sys_var_general_log_path,  SHOW_SYS},
   {sys_group_concat_max_len.name, (char*) &sys_group_concat_max_len,  SHOW_SYS},
+  {sys_hostname.name,         (char*) &sys_hostname,                SHOW_SYS},
   {sys_have_compress.name,    (char*) &have_compress,               SHOW_HAVE},
   {sys_have_crypt.name,       (char*) &have_crypt,                  SHOW_HAVE},
   {sys_have_csv_db.name,      (char*) &have_csv_db,                 SHOW_HAVE},