Too many open files (more than 1048576)

I get this error when backing up a database with lots of tables (really lots). I know about ulimit and have set the maximum number of open files at 1048576 (kernel hard coded maximum), but last night we exceeded this number.

Does anybody know:

  • If we can configure xtrabackup in a way that will open less tables (or less concurrently)?
  • How we can increase the kernel limit of 1048576?