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Just curious, are these two completely equivalent?

chmod +x file
chmod 0755 file

Thanks :-)

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No, because +x just adds x to the current mask for everybody, not influencing rw, while 0755 changes the whole mask. –  Ondrej Kupka Mar 25 '12 at 13:07
    
-1 You would have found this out if you read the man page for chmod and possibly the wpedia page for Filesystem permissions. –  Eroen Apr 19 '12 at 15:55

4 Answers 4

up vote 3 down vote accepted

chmod 0755 file is equivalent to u=rwx (4+2+1),go=rx (4+1 & 4+1). The 0 specifies default special modes (see comment below). See wikipedia for more info (including tables describing u,g,o,a and r,w,x,s,t,).

So in other words: No, they're not equivalent since 0755 contains more flags.

See also: chmod man page

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That's not accurate. The 0 specifies set UID (4), get GID (2) and sticky bit (1) in the first of the 4 numbers. If omitted, it assumes a padded 0 on the front. –  iandouglas Mar 25 '12 at 13:12
    
@iandouglas But "if omitted, it assumes a padded 0 on the front", should then mean that 0 is the default? So in other words, you're just saying that it should say "no special special modes" ? –  keyser5053 Mar 25 '12 at 13:26
    
To my knowledge, yes, 0 is an implied default, so "755" should be the same as "0755" –  iandouglas Mar 25 '12 at 13:54
    
@iandouglas post edited –  keyser5053 Mar 25 '12 at 13:57

No, because chmod 755 also sets various read and write flags.

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Assuming your file was already chmod 644, then, yes, they are effectively equal. It's better to explicitly list the bits you want to set though, using something like a+x

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Chmod number sets the permissions to exactly that number. Chmod relative only changes the requested bits. A file whose permissions were 000 before chmod +x will now be 111.

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