Questions tagged [permissions]

Permissions are the Unix way of controlling access to resources such as files, directories and devices and may be specified for an owner, group, or all users.

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388
votes
8answers
653k views

How do I copy a folder keeping owners and permissions intact?

So I was going to back up my home folder by copying it to an external drive as follows: sudo cp -r /home/my_home /media/backup/my_home With the result that all folders on the external drives are now ...
387
votes
8answers
269k views

Execute vs Read bit. How do directory permissions in Linux work?

In my CMS, I noticed that directories need the executable bit (+x) set for the user to open them. Why is the execute permission required to read a directory, and how do directory permissions in Linux ...
260
votes
4answers
427k views

How to set default file permissions for all folders/files in a directory?

I want to set a folder such that anything created within it (directories, files) inherit default permissions and group. Lets call the group "media". And also, the folders/files created within the ...
182
votes
4answers
89k views

Why do we use su - and not just su?

I don't understand why su - is preferred over su to login as root.
162
votes
4answers
98k views

Do the parent directory's permissions matter when accessing a subdirectory?

If I have a root folder with some restrictive permission, let's say 600, and if the child folders/files have 777 permission will everybody be able to read/write/execute the child file even though the ...
156
votes
9answers
47k 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 ...
150
votes
3answers
279k views

How does the sticky bit work?

SUID The sticky bit applied to executable programs flagging the system to keep an image of the program in memory after the program finished running. But I don't know that what it's stored in memory....
131
votes
3answers
189k views

Make all new files in a directory accessible to a group

Suppose I have two users Alice and Bob and a group GROUPNAME and a folder foo, both users are members of GROUPNAME (using Linux and ext3). If I save as user Alice a file under foo, the permissions ...
126
votes
6answers
104k views

Clone ownership and permissions from another file?

Is there a command or flag to clone the user/group ownership and permissions on a file from another file? To make the perms and ownership exactly those of another file?
124
votes
1answer
185k views

How to skip “permission denied” errors when running find in Linux? [duplicate]

Possible Duplicate: How do I remove “permission denied” printout statements from the find program? When I run this command in Linux (SuSE): find / -name ant I get many error ...
124
votes
7answers
42k views

What does the @ mean in ls -l?

I am using Mac OSX. When I type ls -l I see something like drwxr-xr-x@ 12 xonic staff 408 22 Jun 19:00 . drwxr-xr-x 9 xonic staff 306 22 Jun 19:42 .. -rwxrwxrwx@ 1 xonic staff 6148 25 ...
113
votes
7answers
17k views

Redirecting stdout to a file you don't have write permission on

When you attempt to modify a file without having write permissions on it, you get an error: > touch /tmp/foo && sudo chown root /tmp/foo > echo test > /tmp/foo zsh: permission denied:...
105
votes
8answers
211k views

File permission issues with shared folders under Virtual Box (Ubuntu Guest, Windows Host)

I am using Ubuntu on Virtual Box and I have a folder which is shared between the host (Windows) and the VM (Ubuntu). When I open any file in the share folder in Ubuntu, I can not change it as its ...
102
votes
2answers
263k views

Mount cifs Network Drive: write permissions and chown

I have access to a cifs network drive. When I mount it under my OSX machine, I can read and write from and to it. When I mount the drive in ubuntu, using: sudo mount -t cifs -o username=${USER},...
99
votes
1answer
46k views

What does the “@” (at) symbol mean on OSX ls? [duplicate]

When I check permission of less files from the command line on my Snow Leopard OSX system using Bash I see -rw-r--r--@ for certain files and for others I just see -rw-r--r-- What does the @ mean here?
98
votes
2answers
128k views

How can I start the python SimpleHTTPServer on port 80?

I am using this command on Ubuntu but it is starting on port 8080 and I don't have another server running so I'd like it to start on port 80. I saw ways that you could set up a bash script to do ...
93
votes
3answers
73k views

Why can rm remove read-only files?

If I create a file and then change its permissions to 444 (read-only), how come rm can remove it? If I do this: echo test > test.txt chmod 444 test.txt rm test.txt ...rm will ask if I want to ...
88
votes
3answers
193k views

Getting new files to inherit group permissions on Linux

I am having a problem with permissions on a Linux server. I am used to BSD. When a directory is owned by a group the user who owns it isn't in such as www-data, files created in it will be owned by ...
79
votes
3answers
141k views

What are correct permissions for /tmp ? I unintentionally set it all public recursively

I have abused sudo. I have created a really really short life temporary directory that I wanted to share between some users for a few hours... and I named this directory /some/path/tmp Unfortunately ...
75
votes
3answers
68k views

Why can't a normal user `chown` a file?

Why is the chown command root-only? Why can't non-root users use chown to give away files they own?
71
votes
5answers
252k views

What is the right file permission for a .pem file to SSH and SCP

I have tried to SSH into my AWS Ubuntu server and copy the directory to my local machine. Throughout the process I experience different file permission errors (noted below). Is there one specific ...
70
votes
5answers
59k 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) ...
67
votes
4answers
71k views

What's the difference between “s” and “S” in ls -la?

When I ls -la, it prints many attributes. Something like this: -rwSrwSr-- 1 www-data www-data 45 2012-01-04 05:17 README Shamefully, I have to confess I don't know the exact meaning of each ...
66
votes
9answers
56k views

Can a script be executable but not readable?

Is it possible to execute a script if there is no permission to read it? In root mode, I made a script and I want the other user to execute this script but not read it. I did chmod to forbid read and ...
65
votes
1answer
4k views

What did the sticky bit originally do when applied to files?

In various places one can see the "sticky bit" accused of nowadays being a complete misnomer, as its functionality nowadays is to affect the write permissions on directories and act as a restricted ...
61
votes
1answer
121k views

Preserve the permissions with rsync

Let's say I have a file a.txt in LINUX with permission of 0664. When I use rsync to copy the file to my Mac with rsync -r -t -v LINUX MAC, the file's permission becomes 0644. How can I keep the ...
60
votes
9answers
160k views

Is there a way to stop having to write 'sudo' for every little thing in Linux?

I'm going to be doing a fair amount of PHP work shortly, and I'm interested in learning RoR, so I installed Linux Mint 12 in my VirtualBox. The most frustrating aspect of the switch, so far, has been ...
60
votes
5answers
108k views

How to check if a user can access a given file?

*nix user permissions are really simple, but things can get messy when you have to take in account all the parent directory access before reaching a given file. How can I check if the user has enough ...
58
votes
8answers
10k views

Why does Bash's source not need the execution bit?

With Bash's source it is possible to execute a script without an execution bit set. This is documented and expected behaviour, but isn't this against the use of an execution bit? I know, that source ...
55
votes
2answers
92k views

SSH and home directory permissions

It took me hours to solve this SSH problem with one of my class accounts on my school's servers. I couldn't ssh into one particular class account without entering my password, while passwordless ...
52
votes
3answers
14k views

Why is rm allowed to delete a file under ownership of a different user?

From the post Why can rm remove read-only files? I understand that rm just needs write permission on directory to remove the file. But I find it hard to digest the behaviour where we can easily delete ...
51
votes
3answers
65k views

How to change ownership from symbolic links?

I am facing some issue with creating soft links. Following is the original file. $ ls -l /etc/init.d/jboss -rwxr-xr-x 1 askar admin 4972 Mar 11 2014 /etc/init.d/jboss Link creation is failing with ...
51
votes
4answers
62k views

Is there any difference between mode value 0777 and 777

I saw a code change at work, where the mode values were changed from 777 to 0777 to make nfs setattr work. What is the difference in the 2 values?
51
votes
2answers
78k views

What does the 'd' mean in ls -al results and what is that slot called? [duplicate]

In Linux, what does the d mean in the first position of drwxr-xr-x? And what are all of the possible letters that could be there, and what do they mean? I'm trying to learn more about the Linux file ...
48
votes
3answers
126k views

Unable to delete file, even when running as root

I am in the process of migrating a machine from RHEL 4 to 5. Rather than actually do an upgrade we have created a new VM (both machines are in a cloud) and I am in the process of copying across data ...
45
votes
4answers
129k 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 ...
44
votes
3answers
162k views

Run ./script.sh vs bash script.sh - permission denied

When I try to run ./script.sh I got Permission denied but when I run bash script.sh everything is fine. What did I do wrong?
44
votes
4answers
55k views

File Permissions mode ending in @ or +

I was changing file permissions and I noticed that some of the permissions modes ended in @ as in -rw-r--r--@, or a + as in drwxr-x---+. I've looked at the man pages for chmod and chown, and searched ...
44
votes
2answers
55k views

Uppercase S in permissions of a folder

What does the letter S mean below? The file in question is a folder.                                     &...
43
votes
5answers
37k views

How to recursively remove execute permissions from files without touching folders?

I made a backup to an NTFS drive, and well, this backup really proved necessary. However, the NTFS drive messed up permissions. I'd like to restore them to normal w/o manually fixing each and every ...
42
votes
4answers
63k views

Is there any way to prevent deletion of certain files from user owned directory?

Let's say user has Directory1 and it contains File1 File2 CantBeDeletedFile How to make so the user would never be allowed to delete the CantBeDeletedFile? If I change the ownership of Directory1 and ...
41
votes
3answers
52k views

How to apply changes of newly added user groups without needing to reboot? [duplicate]

Assume I'm logged in with user takpar: takpar@skyspace:/$ As root, I've added takpar as a member of group webdev using: # usermod -a -G webdev takpar But it seems it has not been applied, because ...
40
votes
3answers
4k views

Why is the “ls” command showing permissions of files in a FAT32 partition?

I believe that the FAT32 file system does not support file permissions, however when I do ls -l on a FAT32 partition, ls -l shows that the files have permissions: -rw-r--r-- 1 john john 11 Mar 20 15:...
39
votes
2answers
39k views

How to insert text into a root-owned file using sudo? [duplicate]

Possible Duplicate: Redirecting stdout to a file you don't have write permission on Running a command like sudo echo 'text' >> /file.txt fails with: bash: /file.txt: Permission denied
39
votes
3answers
3k views

How does vim steal root owned files?

Witness the following: sh-3.2$ mkdir testcase sh-3.2$ cd testcase sh-3.2$ sudo touch temp sh-3.2$ ls -al total 0 drwxr-xr-x 3 glen staff 102 19 Dec 12:38 . drwxr-xr-x 12 glen staff 408 19 Dec ...
38
votes
9answers
83k 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 ...
38
votes
4answers
98k views

“rsync: failed to set permissions on …” error with rsync -a or -p option

When I use the -a option as is asked and answered in Preserve the permissions with rsync, I got a lot of "rsync: failed to set permissions on" errors. rsync: failed to set permissions on "/ata/text/...
38
votes
2answers
88k views

What is nobody user and group?

On my server (Synology DS212) some files and folders have nobody nobody users and groups. What are the characteristics of this user and group? Who can write of read this file? How can I change it ? ...
37
votes
3answers
35k views

systemd: permission issue with mkdir & ExecStartPre

I've got a problem with this (shortened) systemd service file: [Unit] Description=control FOO daemon After=syslog.target network.target [Service] Type=forking User=FOOd Group=FOO ExecStartPre=/bin/...
37
votes
3answers
40k views

Can files be created with permissions set on the command line?

When creating directories, mkdir -m <mode> <dir> provides for creating one or more directories with the given mode/permissions set (atomically). Is there an equivalent for creating files, ...