ORA-27040: file create error, unable to create file

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It's not the first time i write about the stack of errors returned by data pump operations and ORA-31641 in particular, however the error messages may vary slightly with the operating system. For instance the following error stack is returned on XE running on top of Ubuntu, whereas the previously linked page refers to an error condition occurring on XE for Windows.

expdp user/pwd directory=EXPDIR dumpfile=dump.dp tables=emp,dept nologfile=Y

ORA-39001: invalid argument value
ORA-39000: bad dump file specification
ORA-31641: unable to create dump file "/home/flavio/documents/dump.dp"
ORA-27040: file create error, unable to create file
Linux Error: 13: Permission denied

The problem is caused by the missing privileges of user oracle on the directory pointed to by EXPDIR.
EXPDIR is pointing to /home/flavio/documents.

ls -ld /home/flavio/documents

drwxr-xr-x 4 flavio flavio 4096 2009-04-10 19:00 /home/flavio/documents/

As you see the directory belongs to user flavio, group flavio, moreover no write privileges are granted other than to the directory owner. Now, as Oracle processes are running under the user oracle, in order to be able to dump a file in this directory we have two possibilities:

1. to change the other group permissions on the directory i.e. by executing chmod o+w documents.
   
2. to add user oracle to group flavio and grant write permissions on documents to group flavio by executing sudo usermod -a -G flavio oracle; chmod g+w documents.

Note that option #1 will work instantly while option #2 requires a db restart. If you do not restart the db, you will still get the permission denied error. In either case, the db user must have READ and WRITE permissions on EXPDIR or hold CREATE ANY DIRECTORY privilege.

Whether the optimal solution is either of the two options above it really depends on the application security requirements.
In the end may be it's better to create a public directory where everybody can dump files freely or create a shared directory EXPDIR where only oracle can create files and users belonging to a datapump group can read them. This approach avoids tampering with the existing permissions on user's private folders and it doesn't require a db restart.

Final notes: while looking for the Optimal Flexible Architecture document, i realized that dpdump is nowhere to be found in the installation documents through version 11gR1. This directory is created at time of installation and it is an OFA directory, no matter what the books say or don't. Directory object DATA_PUMP_DIR, which is the default directory for data pump operations, indeed maps to dpdump.
If i remember correctly in 10gR2 the directory object is automatically created at installation time whilst in 10gR1 you need to create it manually.

See message translations for ORA-27040 and search additional resources.