Understanding chmod: The Difference Between u+x and +x

The chmod command is used to assign permissions on files and directories within a Linux system. Chmod can accept many varying syntaxes, such as symbolic mode and absolute mode, therefore it can be a little confusing when learning all the different ways that chmod can be used. When it comes to granting a user execute permissions, the u+x and +x options are often used because of their simple and straightforward syntax. But do you know the difference between these two options?

In this tutorial, you will learn about the differences between chmod options u+x and +x on the Linux command line. We will also cover a basic rundown of this command syntax in general, so you gain a fundamental understanding of how to utilize chmod quickly and efficiently for assigning read, write, and execute permissions to users or groups on your Linux system.

In this tutorial you will learn:

• The difference between u+x and +x options for chmod
• How to use chmod symbolic syntax to assign permissions to user, group, and other accounts
• How does the umask setting affect the chmod +x command?

Software Requirements and Linux Command Line Conventions

Category	Requirements, Conventions or Software Version Used
System	Any Linux distro
Software	chmod, umask
Other	Privileged access to your Linux system as root or via the sudo command.
Conventions	# – requires given linux commands to be executed with root privileges either directly as a root user or by use of sudo command $ – requires given linux commands to be executed as a regular non-privileged user

The Difference Between chmod Options u+x and +x

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Short Answer

In case you are in a hurry and do not care about the nuances behind the chmod command, here is the answer you are looking for:

• u+x will assign execute permissions for the user (owner) of the file
• +x will assign execute permissions on the file for all users on your system

Longer Explanation

Let’s start by taking a look at the following command:

$ chmod u+x file.sh

Now we can break it down starting with the first option, which is u. When assigning permissions to a file with chmod and symbolic mode syntax, we can use u to assign permissions for the current user (owner) of the file. A list of total options includes:

• u = the current user / owner
• g = the group that owns the file
• o = all other user accounts
• a = all users (user; group; and all others combined)

After specifying who we want to assign permissions for (either user, group, others, or all), the next character in our options is the + plus sign. This (intuitively) indicates that we are adding permissions. Since the + symbol comes after the u letter, we know that we are adding permissions for the user. In this spot, we could use:

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• + = add permissions
• - = take away permissions
• = = assign specified permissions

Finally, the last character in our options is the x, which represents execute permissions. Now that we have broken down the meaning behind each character, we can determine that the u+x options are adding execute permissions for the user of the file. Keep in mind that the following options can be used for this part of the options:

• r = read permissions
• w = write permissions
• x = execute permissions

So, what does it mean if we specify +x in our chmod options, without explicitly specifying who we want to add the execute permissions for?

$ chmod +x file.sh

In most situations (see below for which ones), using +x is the equivalent to using a+x. In other words, it will assign execute permissions for all users (user, group, and all others).

Varying umask Values Will Yield Different Results

There is one big caveat to the answer above, thanks to a Linux system’s umask setting.

$ umask
0002

A umask setting of 0002, such as in the example above, means that +x will indeed be equivalent to a+x as discussed earlier. A 0002 setting is the default umask on most Linux systems, but you could encounter varying results depending on which distribution you are using or how the system has been configured.

We can get further clarification by adding the -S option to the umask command:

$ umask -S
u=rwx,g=rwx,o=rx

Let’s say that our umask setting is set to 0003 instead. With this setting the a+x and +x for chmod will definitely give us different results.

$ umask 0003

We can then verify the setting:

$ umask
0003
$ umask -S
u=rwx,g=rwx,o=r

With the umask now set to 0003, the chmod +x command will only assign execute permissions to the user and group.

Closing Thoughts

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In this tutorial, we learned about the difference between the u+x and +x options for the chmod command on a Linux system. We also saw a full list of similar options that we can use with the chmod command in order to assign or revoke read, write, and execute permissions on files for the user, group, and other accounts. Finally, we learned about the impact of the umask setting when it comes to assigning permissions on Linux.