Questions tagged [chmod]

chmod is used to change the commonly used read, write, and execute permissions on files. It can change these permission bits for the file owner, the file's group owner, and everyone else. It can also change the more esoteric ‘permissions’ (attributes, reall) like set-user-ID, set-group-ID, and sticky bits.

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32
votes
4answers
28k views

Wrongly set chmod / 777. Problems?

I was trying to run chmod -R 777 ./ but ended up typing chmod -R 777 / and set 777 on my entire machine. What can go wrong? How can I fix it?
66
votes
5answers
56k views

Understanding UNIX permissions and file types

I've never really got how chmod worked up until today. I followed a tutorial that explained a big deal to me. For example, I've read that you've got three different permission groups: owner (u) ...
14
votes
8answers
26k views

Convert ls -l output format to chmod format

Say I have the following output from ls -l: drwxr-xr-x 2 root root 4096 Apr 7 17:21 foo How can I automatically convert this to the format used by chmod? For example: $ echo drwxr-xr-x | chmod-...
155
votes
9answers
44k views

How to chmod without /usr/bin/chmod? [duplicate]

Today I was told a tale by a Unix trainer where the root password got leaked to the students, and one of the fellas removed the execute permission from /usr/bin/chmod itself. How do you recover chmod ...
52
votes
7answers
206k views

How to get permission number by string : -rw-r--r--

I need to set the same chmod, how to get number for -rw-r--r-- ?
36
votes
4answers
15k views

How to recover from a chmod -R 000 /bin?

And now I am unable to chmod it back.. or use any of my other system programs. Luckily this is on a VM I've been toying with, but is there any way to resolve this? The system is Ubuntu Server 12.10. ...
20
votes
4answers
2k views

What is a valid use case for an “execute only” file permission?

I was reading up on chmod and its octal modes. I saw that 1 is execute only. What is a valid use case for an execute only permission? To execute a file, one typically would want read and execute ...
15
votes
1answer
18k views

Why does setuid not work? [duplicate]

I want to ensure that my program can only be run by user xyz using root privilege. To do this, I set the setuid bit with: chmod u+s program1.sh ls -l program1.sh rwsr-x--- 1 root house 1299 May 15 23:...
13
votes
4answers
3k views

vim: create file with +x bit

Is there any way to set +x bit on script while creating? For example I run: vim -some_option_to_make_file_executable script.sh and after saving I can run file without any additional movings. ps. I ...
4
votes
3answers
9k views

Change Folder Permissions

I started off with changing to the folder I want to change permissions for, and that is the opt folder. $ cd /opt/ test@testVM:/opt$ So I tried changing the permissions for this folder now using: ...
19
votes
3answers
12k views

I accidentally chmod -R +x on a directory. How do I restore the correct permissions?

Well, to be specific, it was chmod -R 755. Now every file is executable, which I don't want. I am thinking that I should look at the first two bytes of each file for the #!, but will this cover ...
18
votes
2answers
7k views

How to apply recursively chmod directories without affecting files?

After I apply chmod -R to a directory, permissions are changed for everything within (files and directories). How can I add execute/search (x) permissions to directories without modifying the files?
13
votes
3answers
21k views

Write access without read access

Is it possible for a user to have a write access to a file and not be able to read it? How is it possible? I tried the following commands: debianbox@debian:~/posix/io$ touch filetest debianbox@...
10
votes
2answers
10k views

Difference between chmod vs ACL

I understand chmod and chown and how the permission bits work, but there is another permission system inside Linux, ACL with setfacl and getfacl, so this makes me wonder. What's the difference ...
93
votes
4answers
136k views

Get the chmod numerical value for a file

In FreeBSD and also in Linux, how can I get the numerical chmod value of a file? For example, 644 instead of -rw-r--r--? I need an automatic way for a Bash script.
40
votes
1answer
26k views

What is the first chmod octal digit in a four-digit value for?

Sometimes I see chmod commands that use four octal digits instead of three -- what is the optional first digit for? For example, chmod 777 is equivalent to chmod a+rwx; what's the same command for ...
41
votes
4answers
116k views

'chmod g+s' command

Hello I want to understand the role of the chmod g+s command in Unix. I also would like to know what it does in this particular context: cd /home/canard; touch un; chgrp canard .; chmod g+s .; touch ...
13
votes
3answers
51k views

How to check which Apache group I can use for the web server to write?

I'm trying to make Wordpress work. I currently have this error message: Could not create directory. /var/www/html/wp-content/upgrade/theme_name when trying to upload a theme. This is the permissions ...
8
votes
2answers
8k views

Chmod by Letters Vs Numbers

I was recently asked by a colleague to use chmod with letters instead of numbers. Apart from the obvious readability advantage is there any particular reason to use letters over numbers ?
12
votes
1answer
6k views

Symbolic link permissions don't change with chmod

I have access to a remote Linux machine where every time I create a symbolic link, it is created by default with the following permissions: lrwxrwxrwx If I try to change the permissions of the ...
8
votes
1answer
5k views

Is NTFS under linux able to save a linux file, with its chown and chmod settings?

I'm having some doubts about how to install and allow Linux to correctly read/write to a NTFS formatted harddrive used as backup of various machines (windows included, that's how I need NTFS). For ...
5
votes
4answers
8k views

How can I change all of the contents inside of directory to what the default file ownership and permissions are?

I have moved contents of another drive into my home directory, but the permissions are not what they should be. First, I changed ownership by entering: ~$ sudo chown -R USERME /home/USERHOME/ ...
13
votes
2answers
8k views

recursively change file permission but not directories?

I was doing a mass recursive change of permissions of some files that I had migrated to a unix system. I changed them to ug+rw, but then I found that I could not traverse subdirectories. I looked at ...
9
votes
3answers
38k views

How can I revert a chmod on the etc directory?

I accidentally executed the following command on the etc directory: sudo chmod -R 700 /etc I know that I have done something very wrong. My terminal now prints: I have no name!@ubuntu: /$ How can ...
4
votes
4answers
641 views

Run a given command on every subpath of a long path

Say I have a long path such as: /a/b/c/d/e/f I would like to run a command only on each of the subpaths of the path: e.g. If my command is cmd, I am looking for a one-liner that can do (perhaps ...
2
votes
1answer
695 views

SUID has no effect on directories with Linux

Why does the SUID bit have no effect when applied to directories in Linux? I clearly see that I can set it with 'chmod u+s'. But why does it not have "any" effect. What is the reason for implementing ...
2
votes
1answer
181 views

Still able to read file after changing permissions

I've made a file as root, and written a string in it. Now I've changed mode to "0" like this: root# ls -al transit/ total 4.0K ---------- 1 root root 6 Jan 5 18:15 27050 root# If I try to tail, ...
2
votes
3answers
287 views

User with read access to /home

Pardon my ignorance but I can't seem to come up with a solution to this one. I'd like to create a user that has read access to every user's home catalog located in /home. Do I need acl's for this or ...
2
votes
2answers
7k views

Change all folder permissions with 1 command

Within my web application directory, how can I change all my folder permissions to rwxr-xr-x (755)? And how can I change all file permissions to rw-r--r-- (644)? I want to change all folders and files ...
2
votes
1answer
2k views

No effect of umask and chmod on mounted drives

The windows drives are mounted at boot-time using pysdm. The setting were nls=iso8859-1,users,umask=002,sync,user,dirsync,uid=mtk When I try to change the permission of files using chmod, I don't ...
0
votes
1answer
5k views

Minimum file permissions to rename file

I put a 64-bit ELF file in my unprivileged user's home directory. I wonder which permissions do I need to have only possiblity to rename this file being logged in as unprivileged user. From what I ...
36
votes
4answers
134k views

Change permissions for a symbolic link

I have a symlink with these permissions: lrwxrwxrwx 1 myuser myuser 38 Aug 18 00:36 npm -> ../lib/node_modules/npm/bin/npm-cli.js* The symlink is located in a .tar.gz archive. Now when I ...
37
votes
9answers
77k views

Why use `chmod 644` instead of `chmod u=rw,go=r,…`?

I've been working on *nix for a few years now, and one of the things I just can't get used to is octal permissions in code. Is there some other reason than line length to prefer chmod 644 ... over ...
18
votes
5answers
46k views

Can't apply chmod to a file

I have a file on my HDD, cd /media/celebisait/5AC69788C6976355 There is my file called myFile.tar.gz. I do als -l, -rw------- 2 celebisait celebisait 1387745311 Jun 6 2013 myFile.tar.gz ...
4
votes
3answers
7k views

Why can't I run programs on another partition in Linux?

So for convenience, I store all my data on my Windows partition so that I can access my data easily from both Linux and Windows. However, I tried compiling a C++ program with g++, and found out that I ...
19
votes
1answer
897 views

Why does chmod require disk space? Not-in-place algorithm?

I try to chmod some files and I get the error "disk quota exceeded": It's true that I don't have that much space remaining in the filesystem where I use chmod, namelynfs.mit.edu:/export/evodesign/...
16
votes
5answers
19k views

chmod recursive permission on thousands of files

This is a more general question about 'chmoding' recursively. I have this script which at some point needs to change the permissions recursively in a folder which has a few hundred thousand files. ...
11
votes
2answers
1k views

Use chmod command selectively

I want to set 755 permission on all files and sub-directories under a specific directory, but I want to execute chmod 755 only for those components which does not have 755 permission. find /...
12
votes
4answers
50k views

permissions 755 on /home/<user>/

I am wondering why by default my directory /home/<user>/ has permissions set to 755. This allows other users to enter into directories and read files in my home. Is there any legitimate reason ...
9
votes
1answer
26k views

What does “execute” permission mean on a folder? [duplicate]

I have read this topic, which gave me some info but I feel I am not fully getting it. What does the execute permission actually mean on a folder? I fully understand what it means on a file, but on a ...
6
votes
3answers
755 views

Unix users, groups, and permissions

I don't understand unix users, groups, permissions, etc. For example, things managed by the chmod, chgrp, usermod, groupadd, etc. commands. How do all these things work?
16
votes
3answers
7k views

Why does chmod +w not give write permission to other(o)

When I run chmod +w filename it doesn't give write permission to other, it just gives write permission to user and group. After executing this command chmod +w testfile.txt running ls -l testfile....
11
votes
3answers
11k views

How do Linux permissions work when a process is running as a specific group?

This is something I haven't been able to find much info on so any help would be appreciated. My understanding is thus. Take the following file: -rw-r----- 1 root adm 69524 May 21 17:31 ...
4
votes
1answer
918 views

What is the meaning of the mode mask names from stat(2) and chmod(2)?

The stat calls have a series of symbolic names for the various bits in the mode field. From the stat(2) manual page: The following mask values are defined for the file mode component of the st_mode ...
4
votes
3answers
192 views

What are the conventional file permissions per filetype before umask is applied

I am looking for a list that specifies the conventional file permission of all the different file-types before the umask is applied. I read in man 1p touch that the default for a regular file is: ...
3
votes
1answer
1k views

chmod -R 644 ~/Documents

I recently noticed that all of the files in my ~/Documents were somehow incorrectly given executable status. This proved annoying as trying to opening any file gave me a message box saying it was ...
2
votes
2answers
6k views

Meaning of chmod 1775

Created a folder "Sample_dir" and analysed its permissions. $ mkdir Sample_dir $ ll Sample_dir/ total 36 drwxrwxr-x 2 user user 4096 Jul 1 19:26 ./ drwx------ 71 user user 28672 Jul 1 19:26 ../ ...
1
vote
1answer
1k views

Safe to change owner of OS X system folders?

I'm trying to get Homebrew to work. That program's diagnosis tool gives me these suggestions: You should probably chown /usr/local/etc ... You should probably chown them: /usr/local/...
1
vote
1answer
10k views

reliable way to give all read/write access recursively in CentOS 7

What is the most reliable way to give all users read/write privileges for a given directory, all of its subdirectories, and files in CentOS 7? In an eclipse web application project that uses Maven, ...
7
votes
2answers
573 views

Can't remove a file with file mode bits a+rw

I have a file with the following file mode bits (a+rw): [0] mypc<johndoe>:~>sudo touch /tmp/test [0] mypc<johndoe>:~>sudo chmod a+rw /tmp/test [0] mypc<johndoe>:~>ls -l ...