Different options available for setting the permissions of files and directories in different hosting environments. Show
Permission basicsSetting permissions is one of the most basic elements of web security. Assigning the correct permissions to the files and directories helps prevent data theft and malicious intrusions. Permissions specify who and what can read, write, modify, and access content on your site. There are two different methods to express permissions in Linux. Permissions may be expressed numerically or alphabetically. At Nexcess, we prefer to numeric permissions because they are easier to read. Each file and directory will have three permission categories for all users: owner, group, and other. The owner group identifies the owner of the file or directory. The group identifies entities assigned to the file or directory. The category of other lists all entities who do not fall into the other two categories. There are three permission types: read, write, and execute.
It is critical to know the permissions of your files and directories. To list the contents of a directory and see the permissions, run this command" ls -l The output of this command would show a similar output to the following: -rw-r--r-- 1 user user 418 Oct 20 23:59 index.php The columns in a directory listing like the one above are: permissions, number of links, owner, group, size, timestamp, and file or directory name.
In this example, the directory permissions, -rw-r--r--, can be divided into the three permission categories.
The permissions -rw-r--r-- translate into the numeric value 644. The read and write permissions’ numeric value is added to provide both read and write permissions to the owner category. Only the read permission is added to the group and other categories. This is a breakdown of the combinations possible and the permissions they apply. 7 = 4 + 2 + 1 (read/write/execute) Restricting permissionsWhen setting permissions on your site, only provide the files and directories with as much access as they need. Open permissions like 777 give files and directories the unlimited capacity to modify and execute code, leaving your site vulnerable to attack. Files holding sensitive information should not be openly accessible, otherwise you risk compromising your site’s data and your visitor’s data. For 24-hour assistance any day of the year, contact our Support Team by email or through the Client Portal. On this page:
OverviewUnix-like operating systems, such as Linux, running on shared high-performance computers use settings called permissions to determine who can access and modify the files and directories stored in their file systems. Each file and directory in a file system is assigned "owner" and "group" attributes. Most commonly, by default, the user who creates a file or directory is set as owner of that file or directory. When needed (for example, when a member of your research team leaves), the system's root administrator can change the user attribute for files and directories. The group designation can be used to grant teammates and/or collaborators shared access to an owner's files and directories, and provides a convenient way to grant access to multiple users. View file permissionsTo view the permissions for all files in a directory, use the For example, if you enter: ls -lah You should see output similar to the following: -rw-r--r-- 1 user1 group1 62 Jan 15 16:10 myfile.txt drwxr-xr-x 2 user1 group1 2048 Jan 15 17:10 Example In the output example above, the first character in each line indicates whether the listed object is a file or a directory. Directories are indicated by a ( The letters
Note the multiple instances of
Change file permissionsTo change file and directory permissions, use the command There are two basic ways of using Symbolic methodThe first and probably easiest way is the relative (or symbolic) method, which lets you specify permissions with single letter abbreviations. A
For example, to add permission for everyone to read a file in the current directory named chmod a+r myfile The Note: This assumes that everyone already has access to the directory where If you omit the access class, it's assumed to be all, so you could also enter the previous example as: chmod +r myfile You can also specify multiple classes and types with a single command. For example, to remove read and write permission for group and other users (leaving only yourself with read and write permission) on a file named chmod go-rw myfile You can also specify that different permissions be added and removed in the same command. For example, to remove write permission and
add execute for all users on chmod a-w+x myfile In each of these examples, the access types that aren't specified are unchanged. The previous command, for example, doesn't change any existing settings specifying whether users besides yourself may have read ( chmod go=r myfile The chmod o-w mydir To do the same for the current directory, you would enter: chmod o-w To change permissions recursively in all subdirectories below the specified directory, add the chmod -R o+x mydir Be careful when setting the
permissions of directories, particularly your home directory; you don't want to lock yourself out by removing your own access. Also, you must have execute permission on a directory to switch ( Absolute form The other way to use the The three numbers are specified in the order: user (or owner), group, and other. Each number is the sum of values that specify read, write, and execute access:
Add the numbers of the permissions you want to give; for example:
You can think of the three digit sequence as the sum of attributes you select from the following table:
Sum all the accesses you wish to permit. For example, to give write and execute privileges to the owner of chmod 744 myfile Some other examples are:
Common issues when sharing data with other usersTo share a file or directory that you own with someone, you can grant read and execute privileges for that user. However, you must also set the same privileges on any parent directories above the item you're sharing; if you don't, the user can't look and change into ( If you think of a file system as a physical place, then permissions work like keys that let you access different directories:
For example, say you want to give someone access to
If someone wanted to run your scripts, you would need to give that person access to every part of chmod +rx /N/u/username/Carbonate/scripts However, a user can't read or access a subdirectory unless the user also has To resolve this, give chmod +x /N/u/username/ chmod +x /N/u/username/Carbonate This will let others move ( Get helpFor more about man chmod What minimum permission must a directory have for a user to both enter the directory and list its contents?The user has read, write and execute permission. Group has read and execute permission on the directory. Nobody else can access it. Note: a directory must have both r and x permissions if the files it contains are to be accessed.
What does the 777 permission means in a directory?777 - all can read/write/execute (full access). 755 - owner can read/write/execute, group/others can read/execute. 644 - owner can read/write, group/others can read only.
What are the three sets of permissions for a file or directory?There are three basic permissions in each set: read, write, and execute. For files, those are pretty straightforward: "read" lets you see the file's contents; "write" lets you change the file's contents; and "execute" lets you run the file as a program.
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