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| Owner Rights (u) | Group Rights (g) | Others Rights (o) | |
|---|---|---|---|
| Read (4) | |||
| Write (2) | |||
| Execute (1) |
Use the octal CHMOD Command:chmod 1407 file_nameOR use the symbolic CHMOD Command:chmod a+rwx,u-wx,g-rwx,ug+s,+t,u-s,g-s file_nameChmod Permissions for chmod 1407Chmod owner
Chmod group
Chmod other
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Symbolic notation is used to change the permissions of files and directories relative to their current permissions.
This tool can be used to explore how symbolic notations work.
To use this tool set the current octal value of your file permissions and then select from the checkboxes below to create the target permissions for your file(s).
File Permission's "Symbolic Value", or "Symbolic Notation", is a string made up of 10 characters that represents access granted to users on the system. Each "Symbolic Value" string is broken down into 4 sections. The file type (file or directory), Owner, Group, and Other in that order. The file is the first character (either d or -), while each of the subsequent groups (owner, group, and other) are represented by each subsequent cluster of three characters. In short, a "Symbolic Value" is the "string" based counterpart of a corresponding "Octal Value".
If you are not the owner of the file or directory, become superuser.
Only the current owner or superuser can use the chmod command to change file permissions on a file or directory.
Change permissions in symbolic mode by using the chmod command.
| $ chmod [who] [operator] [permission] [filename] |
| who | Who specifies whose permissions are to be changed |
| operator | Operator specifies the operation to be performed |
| permission | Permission specifies what permissions are to be changed. |
| filename | Specifies the file or directory. |
Verify that the permissions of the file have changed.
| $ ls -l filename |
The chmod command is used to change the permissions of a file or directory. Here are the common chmod symbolic mode permissions:
For example, to add read (r) and write (w) permission to the owner (u) of a file, you would use the command chmod u+rw filename. To remove execute (x) permission from others (o), you would use the command chmod o-x filename.
The table below displays both numeric values and symbolic representations for permissions.
| Numeric | Symbolic | Permission |
| 0 | --- | none |
| 1 | --x | execute only |
| 2 | -w- | write only |
| 3 | -wx | write and execute |
| 4 | r-- | read only |
| 5 | r-x | read and execute |
| 6 | rw- | read and write |
| 7 | rwx | read, write, and execute |
Symbolic notation often provides straightforward ways to modify file and directory permissions, but some shortcuts and tips can make your workflow even more efficient. When you’re working with multiple files in a directory, you might find specific patterns that recur, such as repeatedly assigning read and write permissions to many different user groups. Instead of typing out each permission change, you can leverage shortcuts like the equals sign (==) to overwrite existing permissions in a single stroke, or the plus (=+) and minus (=-) signs to add or remove specific permissions. These shortcuts can save time and reduce errors, especially when managing large directories with numerous files. By getting comfortable with symbolic shortcuts, you can ensure faster, safer, and more deliberate permission changes that remain crystal-clear to everyone on your team.
Chances are, you’ve run into umask without even realizing it. The umask setting is the default permission mask that applies whenever you create a new file or directory. It plays a critical role in your environment by defining which permissions are automatically withheld. For instance, if your umask is set to 022, newly created files won’t have write permissions for the group or others. If your workflow depends on swift file sharing across a team, you might consider adjusting your umask to grant more permissive defaults. Conversely, if security is your top priority, you can set a more restrictive umask to ensure newly created files aren’t immediately visible or modifiable by other users. By understanding how symbolic mode and umask interact, you’ll gain fuller control over your system’s overall security posture while simplifying the steps you take to manage individual permissions later.
Beyond the basic read, write, and execute settings, there are special permissions you can apply with symbolic mode that greatly affect how files and directories behave. The Setuid bit (s) on executable files allows a user to run a program with the permissions of the file owner. This can be instrumental for system-level utilities that need administrative privileges. The Setgid bit (g) works similarly but applies the group ID instead. Meanwhile, the Sticky Bit (t) on directories ensures that only the file’s owner can delete or rename it, even if other users have write permissions in that directory. Mastering these symbolic settings’ll enhance your system’s security stance and optimize multi-user collaboration processes in shared directories.
When you’re granting or restricting permissions across entire directory trees, recursively applying chmod is a huge convenience. However, it also calls for extra caution—one misapplied command can drastically change permissions for all contained files and subdirectories. The symbolic mode still works efficiently here, letting you add, remove, or set permissions in a controlled manner. It might be beneficial, for example, to give a group execute permission throughout a directory with chmod -R g+x [directory name]. Always remember to double-check which user or group you’re changing and consider the potential security implications of large-scale permission modifications. Recursive chmod is indispensable, but using it thoughtfully ensures you don’t expose sensitive files to the wrong people or break system functionality.
Sometimes, you can add read permission to one group while removing execute permission from another, all in the same command. Symbolic mode supports chaining multiple operations by separating them with commas (,). For example, chmod u+r,g-w,o+x fileName is a single command that assigns read permission to the owner, removes write permission from the group, and grants execute permission to others. This granular control is especially valuable when you’re juggling multiple roles and unique permission setups. Combining multiple symbolic instructions reduces the chance of overlooking one group’s needs or applying redundant commands. It’s a streamlined way to maintain clarity and control over every aspect of your file’s accessibility.
Sometimes, you need to go beyond the traditional user-group-other permissions model. Access Control Lists (ACLs) offer a more fine-grained permission system that can complement symbolic mode when you’re dealing with advanced or specialized security requirements. ACLs allow you to specify permissions for multiple individual users or groups, without forcing you to stick to the three-tiered approach. For instance, you could grant read and execute permissions to a specific user outside your primary group while keeping everyone else restricted. Although not strictly part of chmod symbolic notation, ACLs integrate seamlessly with your existing permission schema. By understanding how symbolic mode and ACLs can coexist, you can build a layered security model that covers virtually every scenario, from simple personal directories to multi-department, shared servers.
Even experienced system administrators can slip up when applying chmod using symbolic mode, especially under time pressure. One common mistake is setting overly permissive rights in public directories, inadvertently exposing sensitive files to everyone on the system. Another error is forgetting about the default umask, which might undo your carefully designed permissions strategy if not aligned correctly. Additionally, ignoring hidden files (often those starting with a dot) can leave behind security holes if you assume everything was changed when it wasn’t. To avoid these pitfalls, take a structured approach: always confirm your current permissions, test changes in a controlled environment if possible, and keep a close eye on symbolic syntax to ensure you’re applying the correct operations to the correct user or group.
As software development cycles accelerate, managing file permissions can become a bottleneck if not automated. Symbolic notation blends seamlessly into scripts and pipeline stages, letting you quickly enforce consistent permissions across build artifacts, container images, and deployment packages. For instance, you can add a step in your continuous integration (CI) workflow to apply a specific permission set to newly generated log files, preventing accidental overwrites or unauthorized access. This step ensures each environment (development, staging, and production) follows the same rules and mitigates the “it works on my machine” syndrome. By weaving symbolic chmod commands into your DevOps processes, you’ll build a more reliable, scalable system that’s easier to secure and maintain.
I think it is inevitable that people program poorly. Training will not substantially help matters. We have to learn to live with it.
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