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I am reading and following examples in MySQL 5.1 Plugin Development. After compiling and moving a .so file (think DLL or Assembly file in Windows) into MySQL plugin directory, I got this message when I tried to create a UDF (User Defined Function):

mysql> create function udf_staticexample returns integer soname 'udf_staticexample.so';
ERROR 1126 (HY000): Can't open shared library 'udf_staticexample.so' (errno: 0 /usr/lib/mysql/plugin/udf_staticexample.so: failed to map segment from shared object: Permission denied)

This is caused by the fact that the .so shared object file is not in the right SELinux security context:

[root@asusfedora plugin]# ll -Z
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_archive.so -> ha_archive.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_archive.so.0 -> ha_archive.so.0.0.0
-rwxr-xr-x. root root system_u:object_r:lib_t:s0       ha_archive.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_blackhole.so -> ha_blackhole.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_blackhole.so.0 -> ha_blackhole.so.0.0.0
-rwxr-xr-x. root root system_u:object_r:lib_t:s0       ha_blackhole.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_example.so -> ha_example.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_example.so.0 -> ha_example.so.0.0.0
-rwxr-xr-x. root root system_u:object_r:lib_t:s0       ha_example.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_federated.so -> ha_federated.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_federated.so.0 -> ha_federated.so.0.0.0
-rwxr-xr-x. root root system_u:object_r:lib_t:s0       ha_federated.so.0.0.0
-rwxr-xr-x. root root unconfined_u:object_r:user_home_t:s0 udf_staticexample.so

To fix this, use chcon –reference to change the security context of the file in question to a referenced file, like this:

[root@asusfedora plugin]# chcon --reference=/usr/lib/mysql/plugin/ha_archive.so /usr/lib/mysql/plugin/udf_staticexample.so
[root@asusfedora plugin]# ll -Z
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_archive.so -> ha_archive.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_archive.so.0 -> ha_archive.so.0.0.0
-rwxr-xr-x. root root system_u:object_r:lib_t:s0       ha_archive.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_blackhole.so -> ha_blackhole.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_blackhole.so.0 -> ha_blackhole.so.0.0.0
-rwxr-xr-x. root root system_u:object_r:lib_t:s0       ha_blackhole.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_example.so -> ha_example.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_example.so.0 -> ha_example.so.0.0.0
-rwxr-xr-x. root root system_u:object_r:lib_t:s0       ha_example.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_federated.so -> ha_federated.so.0.0.0
lrwxrwxrwx. root root system_u:object_r:lib_t:s0       ha_federated.so.0 -> ha_federated.so.0.0.0
-rwxr-xr-x. root root system_u:object_r:lib_t:s0       ha_federated.so.0.0.0
-rwxr-xr-x. root root system_u:object_r:lib_t:s0       udf_staticexample.so

All is well afterwards.

mysql> create function udf_staticexample returns integer soname 'udf_staticexample.so';
Query OK, 0 rows affected (0.00 sec)
mysql> select udf_staticexample();
+---------------------+
| udf_staticexample() |
+---------------------+
|              318749 |
+---------------------+
1 row in set (0.00 sec)