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 ...

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131
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9answers
20k views

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

Today I was told a tale by a Unix trainer, a tale 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 ...
35
votes
2answers
47k 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.
29
votes
5answers
12k views

Understanding UNIX permissions and their attributes

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) ...
29
votes
4answers
9k 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. ...
29
votes
9answers
25k 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 ...
23
votes
4answers
60k 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-- ?
23
votes
7answers
15k views

Is there a web based converter between rwx and the octal version?

I can never remember what the conversion is from something like rw-r--r-- to 644. Is there a simple web based converter between the 2?
23
votes
1answer
12k 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 ...
21
votes
4answers
13k 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?
19
votes
1answer
620 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/...
18
votes
3answers
5k 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 ...
17
votes
2answers
5k 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?
15
votes
3answers
2k views

Purpose of permissions such as 0111 or 0333

What is the purpose of Linux permissions such as 111 or 333 (i.e. the user can execute, but cannot read the file), if the ability to execute does not automatically imply the ability to read?
15
votes
3answers
139k views

Create file in folder: permission denied

I'm a newbie in the GNU/Linux-Ubuntu world. I have a problem copying files to a directory on Ubuntu 12.04. I create a directory in the home directory so that the path where I want to copy to is: /...
14
votes
5answers
24k 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 ...
12
votes
3answers
8k views

chmod + silent mode + how force exit code 0 in spite of error

Is it possible execute chmod and ignore error from command Example ( remark file.txt not exsist to show the example ) When I type chmod 777 file.txt I get error on the output chmod: cannot ...
12
votes
1answer
861 views

Root can't chmod?

In my department we have a small file server with CentOS and samba. I have root access to be able to perform some basic maintenance. Today I was making some folders read-only, so I went ahead and did ...
10
votes
4answers
6k 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. ...
10
votes
1answer
1k views

Make group permissions same as user permissions

I want to set the group permissions for all files and subdirectories within a certain parent directory to whatever the user permission setting for that specific file or directory is. For example, ...
9
votes
8answers
16k 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-...
9
votes
2answers
2k 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. ...
9
votes
4answers
26k 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 ...
9
votes
1answer
19k views

chmod: What does the `+a` parameter mean?

I was following a tutorial and it told me to run sudo chmod +a "SOME_PARAMS" some/dir I was surprised to see that fail telling me chmod: invalid mode: `+a' So I wonder: What does the +a mode ...
9
votes
2answers
5k 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 ...
8
votes
3answers
27k views

Recursive chmod only folders or only files via script or nautilus menu?

This has been discussed before here. What I'd like to know is how to turn these: Recursive chmod only files within this folder: find . -type f -exec chmod 0600 {} \; Recursive chmod only folders ...
8
votes
1answer
4k 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 formated harddrive used as backup of various machines (windows included, that's how I need NTFS). For now ...
7
votes
2answers
19k views

Why does “chmod 1777” and “chmod 3777” both set the sticky bit?

To set the sticky bit on a directory, why do the commands chmod 1777 and chmod 3777 both work?
7
votes
2answers
985 views

How are file permissions calculated?

Using chmod I could set the permissions for a file, but if the parent ( .. ) directory had conflicting permissions, what would happen? And if I create a new file, using touch or something similiar, ...
7
votes
4answers
29k 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 ...
7
votes
3answers
2k 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 ...
7
votes
3answers
23k 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 ...
7
votes
4answers
10k views

When does chmod fail?

Under what circumstances will chmod fail? I looked at the man page but it only specifies usage and doesn't go into details about what circumstances it won't work in. I'd assume chmod will work if: ...
6
votes
3answers
8k 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@...
6
votes
3answers
4k views

File permission with setuid and octal 4000

When we set setuid to a file, we do the following in the terminal: chmod u+s filename This works fine. But the octal number 4000 is always associated with setuid (in books etc). I understand (to ...
6
votes
1answer
380 views

What permissions one needs to run chmod, chown command on a folder/item?

I've always been running chmod/chown commands as a sudo user. But today I wondered if I don't use sudo, what permissions do I need to actually execute chmod/chown command on a folder/file? I've tried ...
6
votes
3answers
13k 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 ...
6
votes
1answer
7k views

Difference between “chmod 775” and “chmod 2755”

What is the difference between "chmod 775" and "chmod 2755"?
5
votes
2answers
2k views

What is the result of running `chmod 7` on a file?

I know chmod 777 allows read, write, and execute for user, group, and others but what if I just do chmod 7? Is that only rwx for the user?
5
votes
5answers
2k views

What are the root permissions for a file?

If I type: ls -l file.txt I see that the rights for that file are equivalent to "456": 4 = owner (r--) 5 = group (r-x) 6 = others (rw-) Which the rights for root in this case? Does it have 777? ...
5
votes
2answers
4k views

execute bit on directories, but not files [duplicate]

Possible Duplicate: How to apply recursively chmod directories without affecting files? What is the command to apply execute permission for directories (for traversal), but leave the execute ...
5
votes
4answers
1k views

recursively chmod

I was trying to chmod folders and files with: find . -type d -exec chmod 755 {} \; find . -type f -exec chmod 644 {} \; But I was wondering: How to do it in one line using find and excluding the ...
5
votes
2answers
4k views

If I change permissions on a tar file, will that apply to the files inside it?

I have a script that runs regularly via cron, that creates a tar.gz file for the purpose of backing up a directory. For reasons beyond my control, the only user who can execute the script via cron is ...
5
votes
1answer
4k 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:...
5
votes
3answers
533 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?
5
votes
3answers
22k views

Giving PHP permission to write to files and folders

UPDATED FOR FURTHER CLARITY: According to http://expressionengine.com/user_guide/installation/installation.html, it says: For most Unix hosts the following is typical, but you may check with your ...
5
votes
2answers
2k views

Directory special permission problem

When I write: chmod g=rws,u=rwx,o=rx folder_name I get: drwxrwSr-x But S is not the same as s, right?
5
votes
2answers
567 views

Is it possible to represent the +X symbolic permission with an octal value?

Is it possible to represent the +X symbolic permission with an octal value? The chmod(1) man page says: execute/search only if the file is a directory or already has execute permission for some ...
5
votes
1answer
507 views

What is chmod 6050 good for

Recently I came across to command: chmod -R 6050 /usr/lib/hadoop-yarn/bin/container-executor I don't know what that mean? I know file permissions like 777 etc. in a mode rwx for owner group others. ...
5
votes
2answers
3k 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 ?
5
votes
2answers
133 views

Is there a flag corresponding to x/X, but for s with chmod on Linux?

When using chmod (in my case part of coreutils 8.12), and recursively setting the x bit, there exists the convenient X (uppercase letter x), to set the bit only on directories. So if you wanted to ...