In "chmod 4755," what does the 4 do? Using sudo, I got "Permission
denied," but the result was 755.

Doug.
--
When his sweetheart said "Come on, let's settle down,"
Wild Cat raised his head and cried:
"Not bloody likely!" --Cole Porter/G.B. Shaw.

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On 26.08.2019 at 21:24, Doug Laidlaw scribbled:

In "chmod 4755," what does the 4 do? Using sudo, I got "Permission
denied," but the result was 755.

It sets the SUID bit. See...

$ man 2 chmod

--
With respect,
= Aragorn =


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On Mon, 26 Aug 2019 21:24:05 +1000, Doug Laidlaw wrote:

In "chmod 4755," what does the 4 do? Using sudo, I got "Permission
denied," but the result was 755.

The 4 of 4755 specifies "Set user ID"

To quote from man chmod, 6th paragraph under DESCRIPTION:

"A numeric mode is from one to four octal digits (0-7), derived by adding up the bits with values 4, 2, and 1. Omitted digits are assume to
be leading zeros. The first digit selects the set user ID (4) and set
group ID (2) and restricted deletion or sticky (1) attributes. The
second digit selects permissions for the user who owns the file: read
(4), write (2), and execute (1); the third selects permissions for
other users in the file's group, with the same values; and the fourth
for other users not in the file's group, with the same values."

Cheers!

jim b.

--
UNIX is not user-unfriendly, it merely expects users to be computer-
friendly.

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On 26/8/19 10:10 pm, Aragorn wrote:

On 26.08.2019 at 21:24, Doug Laidlaw scribbled:

In "chmod 4755," what does the 4 do? Using sudo, I got "Permission
denied," but the result was 755.

It sets the SUID bit. See...

$ man 2 chmod

Thanks, I just found a log line that says that. Apparently sudo does
not give me high enough permissions.


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On 26/8/19 10:22 pm, Jim Beard wrote:

On Mon, 26 Aug 2019 21:24:05 +1000, Doug Laidlaw wrote:

In "chmod 4755," what does the 4 do? Using sudo, I got "Permission
denied," but the result was 755.

The 4 of 4755 specifies "Set user ID"

To quote from man chmod, 6th paragraph under DESCRIPTION:

"A numeric mode is from one to four octal digits (0-7), derived by adding up the bits with values 4, 2, and 1. Omitted digits are assume to
be leading zeros. The first digit selects the set user ID (4) and set group ID (2) and restricted deletion or sticky (1) attributes. The
second digit selects permissions for the user who owns the file: read
(4), write (2), and execute (1); the third selects permissions for
other users in the file's group, with the same values; and the fourth
for other users not in the file's group, with the same values."

Cheers!

jim b.

Thanks for the explanation, Jim. I had heard of SUID, but had never encountered it before. In this case, a "sandbox" file needed it before
it could be edited. I ran "su -" first, then the change was accepted.
In Windows, of course, the problem didn't arise.


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On 2019-08-26, Doug Laidlaw <laidlaws@hotkey.net.au> wrote:

In "chmod 4755," what does the 4 do? Using sudo, I got "Permission
denied," but the result was 755.

man chmod
explains all the bits.

Doug.

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