What does chmod -u do?2019 Community Moderator ElectionWhy does chmod +w not give write permission to other(o)Is NTFS under linux able to save a linux file, with its chown and chmod settings?chmod -R 644 ~/Documentschmod: What does the `+a` parameter mean?External drive chmod does nothingWhen does chmod fail?invalid mode chmod commandRoot can't chmod?chmod - What does this command do?In Fedora what corresponds to chmod?What is a chmod equivalent of mesg
How can I write humor as character trait?
Why Shazam when there is already Superman?
How to fade a semiplane defined by line?
Do the primes contain an infinite almost arithmetic progression?
What does "Scientists rise up against statistical significance" mean? (Comment in Nature)
Mixing PEX brands
Is this toilet slogan correct usage of the English language?
Does malloc reserve more space while allocating memory?
PTIJ: Haman's bad computer
What is Cash Advance APR?
How much character growth crosses the line into breaking the character
What if a revenant (monster) gains fire resistance?
Need help understanding what a natural log transformation is actually doing and why specific transformations are required for linear regression
Limits and Infinite Integration by Parts
Can a College of Swords bard use a Blade Flourish option on an opportunity attack provoked by their own Dissonant Whispers spell?
What is the evidence for the "tyranny of the majority problem" in a direct democracy context?
Why did the EU agree to delay the Brexit deadline?
How can "mimic phobia" be cured or prevented?
Can a stoichiometric mixture of oxygen and methane exist as a liquid at standard pressure and some (low) temperature?
Why does the Sun have different day lengths, but not the gas giants?
Quoting Keynes in a lecture
Does an advisor owe his/her student anything? Will an advisor keep a PhD student only out of pity?
Why would a new[] expression ever invoke a destructor?
Plot of a tornado-shaped surface
What does chmod -u do?
2019 Community Moderator ElectionWhy does chmod +w not give write permission to other(o)Is NTFS under linux able to save a linux file, with its chown and chmod settings?chmod -R 644 ~/Documentschmod: What does the `+a` parameter mean?External drive chmod does nothingWhen does chmod fail?invalid mode chmod commandRoot can't chmod?chmod - What does this command do?In Fedora what corresponds to chmod?What is a chmod equivalent of mesg
By accident I ran chmod -u filename
and it removed all of the permissions I had on filename
.
The man page does not reference a -u
option. Experimenting I was able to conclude that it removes not all permissions, but just read and execute access, leaving write access intact.
So what does this do exactly?
My conclusion above is wrong, I now think that what it does is remove the permissions that the owner has, from all categories.
I think the behavior is analogous to a=u
, only it is -
instead of =
and a
can be dropped just as it can with, for instance, a+x
.
chmod
New contributor
|
show 1 more comment
By accident I ran chmod -u filename
and it removed all of the permissions I had on filename
.
The man page does not reference a -u
option. Experimenting I was able to conclude that it removes not all permissions, but just read and execute access, leaving write access intact.
So what does this do exactly?
My conclusion above is wrong, I now think that what it does is remove the permissions that the owner has, from all categories.
I think the behavior is analogous to a=u
, only it is -
instead of =
and a
can be dropped just as it can with, for instance, a+x
.
chmod
New contributor
+1 for asking a basic question that is not in the man page.
– jww
2 hours ago
1
"The format of a symbolic mode is[ugoa...][[-+=][perms...]...]
, whereperms
is either zero or more letters from the setrwxXst
, or a single letter from the setugo
" (GNU chmod man page); POSIX is fairly obscure, but defines a "permcopy" production for the same effect.
– Michael Homer
2 hours ago
@MichaelHomer It doesn't say what it does.
– y_wc
2 hours ago
@y_wc "Instead of one or more of these letters, you can specify exactly one of the letters ugo: the permissions granted to the user who owns the file (u
), the permissions granted to other users who are members of the file's group (g
), and the permissions granted to users that are in neither of the two preceding categories (o
)."
– Michael Homer
2 hours ago
Yes, I read that. I don't see that it mentions what it does. It says that I can specify one of those letters. Specifying, for instanceu
, I'll be specifying the permissions granted to the user who owns the file. But it doesn't say what it does. What does specify even mean?
– y_wc
2 hours ago
|
show 1 more comment
By accident I ran chmod -u filename
and it removed all of the permissions I had on filename
.
The man page does not reference a -u
option. Experimenting I was able to conclude that it removes not all permissions, but just read and execute access, leaving write access intact.
So what does this do exactly?
My conclusion above is wrong, I now think that what it does is remove the permissions that the owner has, from all categories.
I think the behavior is analogous to a=u
, only it is -
instead of =
and a
can be dropped just as it can with, for instance, a+x
.
chmod
New contributor
By accident I ran chmod -u filename
and it removed all of the permissions I had on filename
.
The man page does not reference a -u
option. Experimenting I was able to conclude that it removes not all permissions, but just read and execute access, leaving write access intact.
So what does this do exactly?
My conclusion above is wrong, I now think that what it does is remove the permissions that the owner has, from all categories.
I think the behavior is analogous to a=u
, only it is -
instead of =
and a
can be dropped just as it can with, for instance, a+x
.
chmod
chmod
New contributor
New contributor
edited 2 hours ago
y_wc
New contributor
asked 3 hours ago
y_wcy_wc
425
425
New contributor
New contributor
+1 for asking a basic question that is not in the man page.
– jww
2 hours ago
1
"The format of a symbolic mode is[ugoa...][[-+=][perms...]...]
, whereperms
is either zero or more letters from the setrwxXst
, or a single letter from the setugo
" (GNU chmod man page); POSIX is fairly obscure, but defines a "permcopy" production for the same effect.
– Michael Homer
2 hours ago
@MichaelHomer It doesn't say what it does.
– y_wc
2 hours ago
@y_wc "Instead of one or more of these letters, you can specify exactly one of the letters ugo: the permissions granted to the user who owns the file (u
), the permissions granted to other users who are members of the file's group (g
), and the permissions granted to users that are in neither of the two preceding categories (o
)."
– Michael Homer
2 hours ago
Yes, I read that. I don't see that it mentions what it does. It says that I can specify one of those letters. Specifying, for instanceu
, I'll be specifying the permissions granted to the user who owns the file. But it doesn't say what it does. What does specify even mean?
– y_wc
2 hours ago
|
show 1 more comment
+1 for asking a basic question that is not in the man page.
– jww
2 hours ago
1
"The format of a symbolic mode is[ugoa...][[-+=][perms...]...]
, whereperms
is either zero or more letters from the setrwxXst
, or a single letter from the setugo
" (GNU chmod man page); POSIX is fairly obscure, but defines a "permcopy" production for the same effect.
– Michael Homer
2 hours ago
@MichaelHomer It doesn't say what it does.
– y_wc
2 hours ago
@y_wc "Instead of one or more of these letters, you can specify exactly one of the letters ugo: the permissions granted to the user who owns the file (u
), the permissions granted to other users who are members of the file's group (g
), and the permissions granted to users that are in neither of the two preceding categories (o
)."
– Michael Homer
2 hours ago
Yes, I read that. I don't see that it mentions what it does. It says that I can specify one of those letters. Specifying, for instanceu
, I'll be specifying the permissions granted to the user who owns the file. But it doesn't say what it does. What does specify even mean?
– y_wc
2 hours ago
+1 for asking a basic question that is not in the man page.
– jww
2 hours ago
+1 for asking a basic question that is not in the man page.
– jww
2 hours ago
1
1
"The format of a symbolic mode is
[ugoa...][[-+=][perms...]...]
, where perms
is either zero or more letters from the set rwxXst
, or a single letter from the set ugo
" (GNU chmod man page); POSIX is fairly obscure, but defines a "permcopy" production for the same effect.– Michael Homer
2 hours ago
"The format of a symbolic mode is
[ugoa...][[-+=][perms...]...]
, where perms
is either zero or more letters from the set rwxXst
, or a single letter from the set ugo
" (GNU chmod man page); POSIX is fairly obscure, but defines a "permcopy" production for the same effect.– Michael Homer
2 hours ago
@MichaelHomer It doesn't say what it does.
– y_wc
2 hours ago
@MichaelHomer It doesn't say what it does.
– y_wc
2 hours ago
@y_wc "Instead of one or more of these letters, you can specify exactly one of the letters ugo: the permissions granted to the user who owns the file (
u
), the permissions granted to other users who are members of the file's group (g
), and the permissions granted to users that are in neither of the two preceding categories (o
)."– Michael Homer
2 hours ago
@y_wc "Instead of one or more of these letters, you can specify exactly one of the letters ugo: the permissions granted to the user who owns the file (
u
), the permissions granted to other users who are members of the file's group (g
), and the permissions granted to users that are in neither of the two preceding categories (o
)."– Michael Homer
2 hours ago
Yes, I read that. I don't see that it mentions what it does. It says that I can specify one of those letters. Specifying, for instance
u
, I'll be specifying the permissions granted to the user who owns the file. But it doesn't say what it does. What does specify even mean?– y_wc
2 hours ago
Yes, I read that. I don't see that it mentions what it does. It says that I can specify one of those letters. Specifying, for instance
u
, I'll be specifying the permissions granted to the user who owns the file. But it doesn't say what it does. What does specify even mean?– y_wc
2 hours ago
|
show 1 more comment
2 Answers
2
active
oldest
votes
This is not an option, but a standard (but uncommon) way of specifying the permissions. It means to remove (-
) the permissions associated with the file owner (u
), for all users (no preceding u
, g
, or o
). This is documented in the man page.
GNU chmod's man page documents this as:
The format of a symbolic mode is
[ugoa...][[-+=][perms...]...]
, whereperms
is either zero or more letters from the setrwxXst
, or a single letter from the set ugo
and later
Instead of one or more of these letters, you can specify exactly one of the letters ugo: the permissions granted to the user who owns the file (
u
), the permissions granted to other users who are members of the file's group (g
), and the permissions granted to users that are in neither of the two preceding categories (o
)
So -u
means to remove (-
) whatever permissions are currently enabled for the owner (u
) for everybody (equivalently to a-u
, except honouring the current umask). While that's not often going to be very useful, the analogous chmod +u
will sometimes be, to copy the permissions from the owner to others when operating recursively, for example.
It's also documented in POSIX, but more obscurely defined: the permission specification is broadly who[+-=]perms
(or a number), and the effect of those are further specified:
The permcopy symbols
u
,g
, ando
shall represent the current permissions associated with the user, group, and other parts of the file mode bits, respectively. For the remainder of this section,perm
refers to the non-terminalsperm
andpermcopy
in the grammar.
and then
-
...
If who is not specified, the file mode bits represented by perm for the owner, group, and other permissions, except for those with corresponding bits in the file mode creation mask of the invoking process, shall be cleared.
Thanks, Michael. The POSIX documentation is convincing. The GNU however... Please see this comment of mine. I don't see how what comes after "So" follows from what's before.perms
can beu
, that I got. Yes,u
specifies the permissions or the owner. But how does it follow that-u
removes the permissions of the owner (modulusumask
) from all users?
– y_wc
2 hours ago
Because that's what-
always does: it removes the specified permissions from the specified class of users.-u
is exactly analogous to-w
or (closer) tougo-u
.
– Michael Homer
2 hours ago
I was about to say I didn't come here to discuss documentation and that I was happy to just understand what's going on, but the docs just clicked. Thanks.
– y_wc
2 hours ago
Could I trouble you with anotherchmod
documentation question? Let me know if you think this deserves a seperate question. "and = causes them to be added and causes unmentioned bits to be removed except that a directory's unmentioned set user and group ID bits are not affected. " This, to me, is saying that, given a directory whose owner has only write access,chmod u=rx directory
will leave the owner's permissions asrwx
. But that's not what happens, instead they become the expectedr-x
. Am I misinterpreting someting?
– y_wc
2 hours ago
It's saying that the setuid/setgid (s
) bits are left alone if you don't mention them, and anything else you didn't specify is removed.
– Michael Homer
2 hours ago
|
show 1 more comment
The answer is little bit similar to https://unix.stackexchange.com/a/429424/255251.
chmod -u file_name
doesn't removes all permission, but it consider umask
value.
umask
0022
ls -l file
-rwxrwxrwx 1 user user 4 Feb 25 15:17 file
chmod -u file
chmod: file: new permissions are ----w--w-, not ---------
ls -l file
-----w--w- 1 user user 4 Feb 25 15:17 file
Now change umask value
umask 777
chmod 777 file
chmod -u file
chmod: file: new permissions are rwxrwxrwx, not ---------
ls -l file
-rwxrwxrwx 1 user user 4 Feb 25 15:17 file
1
Instructive, good to know and very useful, but I think this isn't really the issue, although it is very much related. Thanks.
– y_wc
2 hours ago
add a comment |
Your Answer
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "106"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
y_wc is a new contributor. Be nice, and check out our Code of Conduct.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f508104%2fwhat-does-chmod-u-do%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
This is not an option, but a standard (but uncommon) way of specifying the permissions. It means to remove (-
) the permissions associated with the file owner (u
), for all users (no preceding u
, g
, or o
). This is documented in the man page.
GNU chmod's man page documents this as:
The format of a symbolic mode is
[ugoa...][[-+=][perms...]...]
, whereperms
is either zero or more letters from the setrwxXst
, or a single letter from the set ugo
and later
Instead of one or more of these letters, you can specify exactly one of the letters ugo: the permissions granted to the user who owns the file (
u
), the permissions granted to other users who are members of the file's group (g
), and the permissions granted to users that are in neither of the two preceding categories (o
)
So -u
means to remove (-
) whatever permissions are currently enabled for the owner (u
) for everybody (equivalently to a-u
, except honouring the current umask). While that's not often going to be very useful, the analogous chmod +u
will sometimes be, to copy the permissions from the owner to others when operating recursively, for example.
It's also documented in POSIX, but more obscurely defined: the permission specification is broadly who[+-=]perms
(or a number), and the effect of those are further specified:
The permcopy symbols
u
,g
, ando
shall represent the current permissions associated with the user, group, and other parts of the file mode bits, respectively. For the remainder of this section,perm
refers to the non-terminalsperm
andpermcopy
in the grammar.
and then
-
...
If who is not specified, the file mode bits represented by perm for the owner, group, and other permissions, except for those with corresponding bits in the file mode creation mask of the invoking process, shall be cleared.
Thanks, Michael. The POSIX documentation is convincing. The GNU however... Please see this comment of mine. I don't see how what comes after "So" follows from what's before.perms
can beu
, that I got. Yes,u
specifies the permissions or the owner. But how does it follow that-u
removes the permissions of the owner (modulusumask
) from all users?
– y_wc
2 hours ago
Because that's what-
always does: it removes the specified permissions from the specified class of users.-u
is exactly analogous to-w
or (closer) tougo-u
.
– Michael Homer
2 hours ago
I was about to say I didn't come here to discuss documentation and that I was happy to just understand what's going on, but the docs just clicked. Thanks.
– y_wc
2 hours ago
Could I trouble you with anotherchmod
documentation question? Let me know if you think this deserves a seperate question. "and = causes them to be added and causes unmentioned bits to be removed except that a directory's unmentioned set user and group ID bits are not affected. " This, to me, is saying that, given a directory whose owner has only write access,chmod u=rx directory
will leave the owner's permissions asrwx
. But that's not what happens, instead they become the expectedr-x
. Am I misinterpreting someting?
– y_wc
2 hours ago
It's saying that the setuid/setgid (s
) bits are left alone if you don't mention them, and anything else you didn't specify is removed.
– Michael Homer
2 hours ago
|
show 1 more comment
This is not an option, but a standard (but uncommon) way of specifying the permissions. It means to remove (-
) the permissions associated with the file owner (u
), for all users (no preceding u
, g
, or o
). This is documented in the man page.
GNU chmod's man page documents this as:
The format of a symbolic mode is
[ugoa...][[-+=][perms...]...]
, whereperms
is either zero or more letters from the setrwxXst
, or a single letter from the set ugo
and later
Instead of one or more of these letters, you can specify exactly one of the letters ugo: the permissions granted to the user who owns the file (
u
), the permissions granted to other users who are members of the file's group (g
), and the permissions granted to users that are in neither of the two preceding categories (o
)
So -u
means to remove (-
) whatever permissions are currently enabled for the owner (u
) for everybody (equivalently to a-u
, except honouring the current umask). While that's not often going to be very useful, the analogous chmod +u
will sometimes be, to copy the permissions from the owner to others when operating recursively, for example.
It's also documented in POSIX, but more obscurely defined: the permission specification is broadly who[+-=]perms
(or a number), and the effect of those are further specified:
The permcopy symbols
u
,g
, ando
shall represent the current permissions associated with the user, group, and other parts of the file mode bits, respectively. For the remainder of this section,perm
refers to the non-terminalsperm
andpermcopy
in the grammar.
and then
-
...
If who is not specified, the file mode bits represented by perm for the owner, group, and other permissions, except for those with corresponding bits in the file mode creation mask of the invoking process, shall be cleared.
Thanks, Michael. The POSIX documentation is convincing. The GNU however... Please see this comment of mine. I don't see how what comes after "So" follows from what's before.perms
can beu
, that I got. Yes,u
specifies the permissions or the owner. But how does it follow that-u
removes the permissions of the owner (modulusumask
) from all users?
– y_wc
2 hours ago
Because that's what-
always does: it removes the specified permissions from the specified class of users.-u
is exactly analogous to-w
or (closer) tougo-u
.
– Michael Homer
2 hours ago
I was about to say I didn't come here to discuss documentation and that I was happy to just understand what's going on, but the docs just clicked. Thanks.
– y_wc
2 hours ago
Could I trouble you with anotherchmod
documentation question? Let me know if you think this deserves a seperate question. "and = causes them to be added and causes unmentioned bits to be removed except that a directory's unmentioned set user and group ID bits are not affected. " This, to me, is saying that, given a directory whose owner has only write access,chmod u=rx directory
will leave the owner's permissions asrwx
. But that's not what happens, instead they become the expectedr-x
. Am I misinterpreting someting?
– y_wc
2 hours ago
It's saying that the setuid/setgid (s
) bits are left alone if you don't mention them, and anything else you didn't specify is removed.
– Michael Homer
2 hours ago
|
show 1 more comment
This is not an option, but a standard (but uncommon) way of specifying the permissions. It means to remove (-
) the permissions associated with the file owner (u
), for all users (no preceding u
, g
, or o
). This is documented in the man page.
GNU chmod's man page documents this as:
The format of a symbolic mode is
[ugoa...][[-+=][perms...]...]
, whereperms
is either zero or more letters from the setrwxXst
, or a single letter from the set ugo
and later
Instead of one or more of these letters, you can specify exactly one of the letters ugo: the permissions granted to the user who owns the file (
u
), the permissions granted to other users who are members of the file's group (g
), and the permissions granted to users that are in neither of the two preceding categories (o
)
So -u
means to remove (-
) whatever permissions are currently enabled for the owner (u
) for everybody (equivalently to a-u
, except honouring the current umask). While that's not often going to be very useful, the analogous chmod +u
will sometimes be, to copy the permissions from the owner to others when operating recursively, for example.
It's also documented in POSIX, but more obscurely defined: the permission specification is broadly who[+-=]perms
(or a number), and the effect of those are further specified:
The permcopy symbols
u
,g
, ando
shall represent the current permissions associated with the user, group, and other parts of the file mode bits, respectively. For the remainder of this section,perm
refers to the non-terminalsperm
andpermcopy
in the grammar.
and then
-
...
If who is not specified, the file mode bits represented by perm for the owner, group, and other permissions, except for those with corresponding bits in the file mode creation mask of the invoking process, shall be cleared.
This is not an option, but a standard (but uncommon) way of specifying the permissions. It means to remove (-
) the permissions associated with the file owner (u
), for all users (no preceding u
, g
, or o
). This is documented in the man page.
GNU chmod's man page documents this as:
The format of a symbolic mode is
[ugoa...][[-+=][perms...]...]
, whereperms
is either zero or more letters from the setrwxXst
, or a single letter from the set ugo
and later
Instead of one or more of these letters, you can specify exactly one of the letters ugo: the permissions granted to the user who owns the file (
u
), the permissions granted to other users who are members of the file's group (g
), and the permissions granted to users that are in neither of the two preceding categories (o
)
So -u
means to remove (-
) whatever permissions are currently enabled for the owner (u
) for everybody (equivalently to a-u
, except honouring the current umask). While that's not often going to be very useful, the analogous chmod +u
will sometimes be, to copy the permissions from the owner to others when operating recursively, for example.
It's also documented in POSIX, but more obscurely defined: the permission specification is broadly who[+-=]perms
(or a number), and the effect of those are further specified:
The permcopy symbols
u
,g
, ando
shall represent the current permissions associated with the user, group, and other parts of the file mode bits, respectively. For the remainder of this section,perm
refers to the non-terminalsperm
andpermcopy
in the grammar.
and then
-
...
If who is not specified, the file mode bits represented by perm for the owner, group, and other permissions, except for those with corresponding bits in the file mode creation mask of the invoking process, shall be cleared.
edited 2 hours ago
answered 2 hours ago
Michael HomerMichael Homer
50.1k8137175
50.1k8137175
Thanks, Michael. The POSIX documentation is convincing. The GNU however... Please see this comment of mine. I don't see how what comes after "So" follows from what's before.perms
can beu
, that I got. Yes,u
specifies the permissions or the owner. But how does it follow that-u
removes the permissions of the owner (modulusumask
) from all users?
– y_wc
2 hours ago
Because that's what-
always does: it removes the specified permissions from the specified class of users.-u
is exactly analogous to-w
or (closer) tougo-u
.
– Michael Homer
2 hours ago
I was about to say I didn't come here to discuss documentation and that I was happy to just understand what's going on, but the docs just clicked. Thanks.
– y_wc
2 hours ago
Could I trouble you with anotherchmod
documentation question? Let me know if you think this deserves a seperate question. "and = causes them to be added and causes unmentioned bits to be removed except that a directory's unmentioned set user and group ID bits are not affected. " This, to me, is saying that, given a directory whose owner has only write access,chmod u=rx directory
will leave the owner's permissions asrwx
. But that's not what happens, instead they become the expectedr-x
. Am I misinterpreting someting?
– y_wc
2 hours ago
It's saying that the setuid/setgid (s
) bits are left alone if you don't mention them, and anything else you didn't specify is removed.
– Michael Homer
2 hours ago
|
show 1 more comment
Thanks, Michael. The POSIX documentation is convincing. The GNU however... Please see this comment of mine. I don't see how what comes after "So" follows from what's before.perms
can beu
, that I got. Yes,u
specifies the permissions or the owner. But how does it follow that-u
removes the permissions of the owner (modulusumask
) from all users?
– y_wc
2 hours ago
Because that's what-
always does: it removes the specified permissions from the specified class of users.-u
is exactly analogous to-w
or (closer) tougo-u
.
– Michael Homer
2 hours ago
I was about to say I didn't come here to discuss documentation and that I was happy to just understand what's going on, but the docs just clicked. Thanks.
– y_wc
2 hours ago
Could I trouble you with anotherchmod
documentation question? Let me know if you think this deserves a seperate question. "and = causes them to be added and causes unmentioned bits to be removed except that a directory's unmentioned set user and group ID bits are not affected. " This, to me, is saying that, given a directory whose owner has only write access,chmod u=rx directory
will leave the owner's permissions asrwx
. But that's not what happens, instead they become the expectedr-x
. Am I misinterpreting someting?
– y_wc
2 hours ago
It's saying that the setuid/setgid (s
) bits are left alone if you don't mention them, and anything else you didn't specify is removed.
– Michael Homer
2 hours ago
Thanks, Michael. The POSIX documentation is convincing. The GNU however... Please see this comment of mine. I don't see how what comes after "So" follows from what's before.
perms
can be u
, that I got. Yes, u
specifies the permissions or the owner. But how does it follow that -u
removes the permissions of the owner (modulus umask
) from all users?– y_wc
2 hours ago
Thanks, Michael. The POSIX documentation is convincing. The GNU however... Please see this comment of mine. I don't see how what comes after "So" follows from what's before.
perms
can be u
, that I got. Yes, u
specifies the permissions or the owner. But how does it follow that -u
removes the permissions of the owner (modulus umask
) from all users?– y_wc
2 hours ago
Because that's what
-
always does: it removes the specified permissions from the specified class of users. -u
is exactly analogous to -w
or (closer) to ugo-u
.– Michael Homer
2 hours ago
Because that's what
-
always does: it removes the specified permissions from the specified class of users. -u
is exactly analogous to -w
or (closer) to ugo-u
.– Michael Homer
2 hours ago
I was about to say I didn't come here to discuss documentation and that I was happy to just understand what's going on, but the docs just clicked. Thanks.
– y_wc
2 hours ago
I was about to say I didn't come here to discuss documentation and that I was happy to just understand what's going on, but the docs just clicked. Thanks.
– y_wc
2 hours ago
Could I trouble you with another
chmod
documentation question? Let me know if you think this deserves a seperate question. "and = causes them to be added and causes unmentioned bits to be removed except that a directory's unmentioned set user and group ID bits are not affected. " This, to me, is saying that, given a directory whose owner has only write access, chmod u=rx directory
will leave the owner's permissions as rwx
. But that's not what happens, instead they become the expected r-x
. Am I misinterpreting someting?– y_wc
2 hours ago
Could I trouble you with another
chmod
documentation question? Let me know if you think this deserves a seperate question. "and = causes them to be added and causes unmentioned bits to be removed except that a directory's unmentioned set user and group ID bits are not affected. " This, to me, is saying that, given a directory whose owner has only write access, chmod u=rx directory
will leave the owner's permissions as rwx
. But that's not what happens, instead they become the expected r-x
. Am I misinterpreting someting?– y_wc
2 hours ago
It's saying that the setuid/setgid (
s
) bits are left alone if you don't mention them, and anything else you didn't specify is removed.– Michael Homer
2 hours ago
It's saying that the setuid/setgid (
s
) bits are left alone if you don't mention them, and anything else you didn't specify is removed.– Michael Homer
2 hours ago
|
show 1 more comment
The answer is little bit similar to https://unix.stackexchange.com/a/429424/255251.
chmod -u file_name
doesn't removes all permission, but it consider umask
value.
umask
0022
ls -l file
-rwxrwxrwx 1 user user 4 Feb 25 15:17 file
chmod -u file
chmod: file: new permissions are ----w--w-, not ---------
ls -l file
-----w--w- 1 user user 4 Feb 25 15:17 file
Now change umask value
umask 777
chmod 777 file
chmod -u file
chmod: file: new permissions are rwxrwxrwx, not ---------
ls -l file
-rwxrwxrwx 1 user user 4 Feb 25 15:17 file
1
Instructive, good to know and very useful, but I think this isn't really the issue, although it is very much related. Thanks.
– y_wc
2 hours ago
add a comment |
The answer is little bit similar to https://unix.stackexchange.com/a/429424/255251.
chmod -u file_name
doesn't removes all permission, but it consider umask
value.
umask
0022
ls -l file
-rwxrwxrwx 1 user user 4 Feb 25 15:17 file
chmod -u file
chmod: file: new permissions are ----w--w-, not ---------
ls -l file
-----w--w- 1 user user 4 Feb 25 15:17 file
Now change umask value
umask 777
chmod 777 file
chmod -u file
chmod: file: new permissions are rwxrwxrwx, not ---------
ls -l file
-rwxrwxrwx 1 user user 4 Feb 25 15:17 file
1
Instructive, good to know and very useful, but I think this isn't really the issue, although it is very much related. Thanks.
– y_wc
2 hours ago
add a comment |
The answer is little bit similar to https://unix.stackexchange.com/a/429424/255251.
chmod -u file_name
doesn't removes all permission, but it consider umask
value.
umask
0022
ls -l file
-rwxrwxrwx 1 user user 4 Feb 25 15:17 file
chmod -u file
chmod: file: new permissions are ----w--w-, not ---------
ls -l file
-----w--w- 1 user user 4 Feb 25 15:17 file
Now change umask value
umask 777
chmod 777 file
chmod -u file
chmod: file: new permissions are rwxrwxrwx, not ---------
ls -l file
-rwxrwxrwx 1 user user 4 Feb 25 15:17 file
The answer is little bit similar to https://unix.stackexchange.com/a/429424/255251.
chmod -u file_name
doesn't removes all permission, but it consider umask
value.
umask
0022
ls -l file
-rwxrwxrwx 1 user user 4 Feb 25 15:17 file
chmod -u file
chmod: file: new permissions are ----w--w-, not ---------
ls -l file
-----w--w- 1 user user 4 Feb 25 15:17 file
Now change umask value
umask 777
chmod 777 file
chmod -u file
chmod: file: new permissions are rwxrwxrwx, not ---------
ls -l file
-rwxrwxrwx 1 user user 4 Feb 25 15:17 file
answered 2 hours ago
Prvt_YadvPrvt_Yadv
2,88031227
2,88031227
1
Instructive, good to know and very useful, but I think this isn't really the issue, although it is very much related. Thanks.
– y_wc
2 hours ago
add a comment |
1
Instructive, good to know and very useful, but I think this isn't really the issue, although it is very much related. Thanks.
– y_wc
2 hours ago
1
1
Instructive, good to know and very useful, but I think this isn't really the issue, although it is very much related. Thanks.
– y_wc
2 hours ago
Instructive, good to know and very useful, but I think this isn't really the issue, although it is very much related. Thanks.
– y_wc
2 hours ago
add a comment |
y_wc is a new contributor. Be nice, and check out our Code of Conduct.
y_wc is a new contributor. Be nice, and check out our Code of Conduct.
y_wc is a new contributor. Be nice, and check out our Code of Conduct.
y_wc is a new contributor. Be nice, and check out our Code of Conduct.
Thanks for contributing an answer to Unix & Linux Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f508104%2fwhat-does-chmod-u-do%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
+1 for asking a basic question that is not in the man page.
– jww
2 hours ago
1
"The format of a symbolic mode is
[ugoa...][[-+=][perms...]...]
, whereperms
is either zero or more letters from the setrwxXst
, or a single letter from the setugo
" (GNU chmod man page); POSIX is fairly obscure, but defines a "permcopy" production for the same effect.– Michael Homer
2 hours ago
@MichaelHomer It doesn't say what it does.
– y_wc
2 hours ago
@y_wc "Instead of one or more of these letters, you can specify exactly one of the letters ugo: the permissions granted to the user who owns the file (
u
), the permissions granted to other users who are members of the file's group (g
), and the permissions granted to users that are in neither of the two preceding categories (o
)."– Michael Homer
2 hours ago
Yes, I read that. I don't see that it mentions what it does. It says that I can specify one of those letters. Specifying, for instance
u
, I'll be specifying the permissions granted to the user who owns the file. But it doesn't say what it does. What does specify even mean?– y_wc
2 hours ago