What to do if you get the semget() failed: Permission denied in wp-cache error

This evening I’ve been playing with the WP-cache plugin. If you install it and find this error:

semget() failed for key 0x152b: Permission denied in...

Then all you have to do is browse to the wp-cache config file which you should find in the /wp-content/ directory.

Take a copy of the file and open it to edit as follows:

change this

to this

Done. Of course you could try the WP-super-cache plugin, which is an improvement over this one – but brings a new set of potential problems. On first install my entire site started delivering blank HTML. Be careful :-)

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Tags: , | Categories: Technical

13 thoughts on “What to do if you get the semget() failed: Permission denied in wp-cache error

  1. Nice tutorial on that. If you try wp-super-cache again make sure you remove wp-content/advanced-cache.php before installing the new plugin. That may have messed things up for you.

  2. John says:

    Hi Richard,

    Love your site! We just got this exact error message and your tutorial made getting it fixed a breeze. I’ll certainly be coming back to check out the rest of your site later.

    We are currently looking at oil rig jobs as an alternative for people who have been laid off due to the current recession.

    Keep up the great work. You’re a life saver for us non-techie types ;-)


  3. frank says:

    Wow thanks!!! This really helped. My site suddenly looked like a picasso. This cleaned it up. And it was a easy fix. great job

  4. Adino says:

    Thanks! This solved the problem for me. I had the same error message whenever I enabled wp-cache, until I removed the comment on the third line.

    My site is working again now.

  5. Nik says:

    Thank you! This worked for me too. I appreciate you posting the fix.

  6. Rob says:

    Thanks! I started getting this problem on my site after running it for a long time without changes. This fixed the problem.

  7. Jim says:

    Hey, thanks very much for this tip. I was just about to remove the wp-cache plugin when I came across this article that fixed the issue.

    The error message I was getting was

    Warning: sem_get() [function.sem-get]: failed for key 0x152b: Permission denied in /www/wp-content/plugins/wp-cache/wp-cache-phase2.php on line 98

    All fixed now thanks to you.

    Many thanks!!


  8. Claire says:

    Thaks so so so much for this info! I was totally stuck until i found your article.
    Thanks for sharing!


  9. Dkat says:

    Thanks! Worked great for me.

  10. joicol says:

    Doesn’t work for me. This //$use_flock is not even in my wp_cache file ?!

  11. THANK YOU! Worked like a charm, as they say.

  12. yuval says:


  13. yuval says:

    Worked nice. just needed to clear the cache at the end of it all.

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