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You need execute permission on a directory to cd to it! Is read not enough? In practice, no. The chdir system call requires execute permission to make that directory the starting point for path searches. According to the chdir (system call, section 2) man page:

For a directory to become the current directory, a process
must have execute (search) access to the directory.

So when trussing the output of a failed cd to a directory with no execute permissions we see:

chdir("lala") Err#13 EACCES [file_dac_search]
chdir(”lala”) Err#13 EACCES [file_dac_search]

and as the man page goes on to say:

EACCES Search permission is denied for any com-
ponent of the path name.

Reading this article explains, that of course you can’t execute a directory but rather, that the execute permission bit is reused for different purposes. Without execute permission on the directory, you can’t stat() any files within the directory. Opening, deleting and other operations on a file first require you to stat() it first, as stat() gives you the files inode. Without the files inode, theres very little you can do with it!

Armed with this knowledge you might feel inspired to check out the source code of this call for yourself!

Tags: cd, chdir()), EACCES, man page, stat()

This entry was posted on Sunday, March 9th, 2008 at 1:41 am and is filed under computing. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.