chmod Command

13 min


In Linux and other Unix-like operating systems, the chmod command is used to change the permissions of a file or directory. The permissions determine who is able to read, write, and execute a file or list the contents of a directory.

The chmod command takes two arguments: the permissions you want to set, and the file or directory whose permissions you want to change.

The permissions are specified using a combination of letters and numbers. There are three types of permissions that can be set: read (r), write (w), and execute (x). These permissions can be set for three different classes of users: the file owner (u), the members of the file’s group (g), and all other users (o).

To specify the permissions, you can use either letters or numbers. Here are some examples:

  • chmod u+x file.txt – This gives the owner of the file execute permissions.
  • chmod g-w file.txt – This removes write permissions for the members of the file’s group.
  • chmod o=r file.txt – This sets read permissions for others.
  • chmod 755 /path/to/directory – This sets read, write and execute permissions for the owner and read and execute permissions for group and others.

You can also use + or - before the letter to add or remove permissions, respectively. And you can also use = to set the permissions to specific value.

You can also use numeric values to represent permissions instead of letters. Each permission is represented by a number: r = 4, w = 2, and x = 1. To specify permissions using numbers, you simply add up the values for the permissions you want to set. For example, rwx permissions can be represented as 7, rw- permissions can be represented as 6 and so on.

You can use chmod on directories as well. When you set permissions on a directory, it changes the permissions for all of the files and subdirectories inside that directory. Also be mindful that using chmod -R you can change recursively all the files and subdirectories inside the directory.

You must be owner of the file or a superuser to run chmod command, otherwise it will fail with permission denied error.

Chmod 777

In Linux and other Unix-like operating systems, the chmod command is used to change the permissions on a file or directory. The 777 is a numeric representation of the permissions that you are setting.

The 777 permissions are made up of three octal digits, each of which corresponds to the read, write, and execute permissions for the file’s owner, the file’s group, and for others (i.e., everyone else).

The permissions are represented by the numbers 0 through 7, with 0 indicating no permissions, and 7 indicating full permissions. The digits for each class of users (i.e., the file’s owner, the file’s group, and others) are added together to form a single three-digit number.

For example, the permissions 777 would give full permissions (i.e., read, write, and execute) to the file’s owner, the file’s group, and others. This is typically not a good idea as it open a security hole, as all the users could delete, change and execute the file, it is a highly recommended practice only use this type of permission in testing environments.

You can use the chmod command followed by the numeric permissions (e.g., 777 or 755) and the name of the file or directory that you want to change the permissions for. For example, to give all users read, write, and execute permissions for a file named example.txt, you would use the following command:

Copy codechmod 777 example.txt

It’s important to note that the chmod command will only work on files and directories that you have permission to change. Also, giving more permissions than needed to files and directories can open security holes, so you should be careful when using chmod and think about the least amount of permissions that your application needs.

Chmod 755

Chmod 755 which gives read and execute permissions to everyone, and read, write and execute permissions to the owner of the file. This is a common permission set for directories, as it allows everyone to navigate the directory, but only the owner can add or remove files.

Chmod 775

The chmod 775 command sets the permissions on a file or directory such that:

  • The owner of the file has read, write, and execute permissions (rwx)
  • Members of the owner’s group have read and execute permissions (r-x)
  • Others have read and execute permissions (r-x)

Here’s an example of how you might use the chmod 775 command:

chmod 775 /path/to/file

This would set the permissions on the file located at /path/to/file such that the owner has read, write, and execute permissions, the owner’s group has read and execute permissions, and others have read and execute permissions.

It is worth noting that the 775 is in octal format, the standard way of representing permissions, where each digit represent the permissions for User, Group, and Others, Each digit is computed by adding together the bits to give the value:

  • rwx is 7 because it is 111 in binary (rwx=4+2+1)
  • rw- is 6 because it is 110 in binary (rw-=4+2+0)
  • r-x is 5 because it is 101 in binary (r-x=4+0+1)

It is also worth noting that these permissions are more permissive than is typically recommended for directories. For instance, directories typically should only be executable but not writable by others and sometimes not readable as well, depending on the use case.

Chmod 770

The command chmod 770 is used to change the file permissions on a Linux or Unix-based system. The 770 at the end of the command represents the permissions that are being assigned.

The permissions are represented as a three-digit octal number, with each digit representing a different component of the file’s permissions. The first digit represents the owner’s permissions, the second digit represents the group’s permissions, and the third digit represents the permissions for everyone else.

The permissions are set using a combination of the numbers 0-7, with each number representing a different level of access. For example, the number 7 gives read, write, and execute permissions, while the number 0 gives no permissions at all.

Here’s an example of how you would use the chmod command to give the owner, group, and everyone else read, write, and execute permissions to a file called example.txt:

Copy codechmod 770 example.txt

This would grant read-write-execute permissions to the owner, read-write-execute to the group and no permission for the other user.

Note that, with 770 permission user can read-write-execute but other user has no permission.

Chmod 744

The command chmod 744 is used to change the file permissions on a Linux or Unix-based system. The 744 at the end of the command represents the permissions that are being assigned.

The permissions are represented as a three-digit octal number, with each digit representing a different component of the file’s permissions. The first digit represents the owner’s permissions, the second digit represents the group’s permissions, and the third digit represents the permissions for everyone else.

In this case, 744 means owner has full access(read, write and execute) permissions, group and others have only read permission. Here’s an example of how you would use the chmod command to give the owner read, write, and execute permissions, and give the group and everyone else only read permissions to a file called example.txt:

Copy codechmod 744 example.txt

You can also use +x to give execute permission to owner, +r to give read permission to others and +w to give write permission to group

Copy codechmod 744 example.txt

This would grant read-write-execute permissions to the owner, read permissions to the group and read permission for the other user.

Note that, with 744 permission user can read-write-execute but group and other user has only read permission

Chmod 644

In the Linux/Unix operating system, the chmod command is used to change the permissions of a file or directory. The permissions can be set using either numeric or symbolic values.

The permission settings are represented by a three-digit octal number, with each digit representing the permissions for the owner, group, and others. Each digit is a combination of the values 4 (read), 2 (write), and 1 (execute).

For example, the permissions value of 644 means:

  • The owner has read and write permissions (6 = 4 (read) + 2 (write))
  • The group and others have only read permissions (4 = 4 (read))

So if you would like to change the permissions of file.txt to 644, you would use the command:

chmod 644 file.txt

Another examples of this command with different permissions

chmod 755 /path/to/directory   #Read, Write and Execute for owner, Read and Execute for group and others

chmod 600 /path/to/file        #Read and Write for owner only

Keep in mind that you can also use Symbolic representation, which is more readable and you don’t need to remember the octal value of each permission.

chmod u+rwx,go+r /path/to/file  # give owner read write execute permissions and group,others read only

Chmod 600

When you run the command chmod 600 file.txt, you are giving the owner of the file read and write permissions (6), and no permissions to others (0). This means that only the owner of the file can read and write to it, and no one else can do anything with it.

Chmod 666

The command chmod 666 file.txt would give read and write permissions to the owner, group and others for the file named file.txt.

This would mean that anyone with access to the file would be able to read and write to it, regardless of whether they are the owner, a member of the group that the file belongs to, or anyone else.

This is generally not recommended for sensitive files, as it allows any user with access to the file system to make changes to it. It is more common to give more restrictive permissions for sensitive files.

Example in a linux command line :

chmod 666 file.txt

This command would give read and write permissions to everyone for file.txt.

Also you can use numeric notation as well

chmod 666 file.txt 

It is equivalent to:

chmod 110 110 file.txt

As mentioned before, be careful when using chmod command with such broad permissions, and think twice before you run it, in order to not inadvertently expose sensitive data.

Chmod 400

The “400” argument passed to the command is an octal representation of the permissions you want to set.

In octal notation, each digit represents the permissions for a different class of users: the owner of the file, members of the file’s group, and all other users. Each digit is a combination of the permissions for the class it represents. The permissions are represented by the numerals 0, 1, 2, 4, and 7. Each digit is a combination of the numbers 0, 1, 2, 4, and 7.

The following are some examples of how chmod 400 can be used:

To set permissions for a file named “example.txt” so that only the owner can read it:

chmod 400 example.txt

This will set the permissions for the owner to “r” (read), and permissions for the group and other users to “—” (no permissions).

To set permissions for a directory named “example” so that only the owner can read and enter it

chmod 400 example

This will set the permissions for the owner to “r” (read and execute), and permissions for the group and other users to “—” (no permissions).

It’s also possible to use numeric notation instead of octal, it can be accomplished by prefixing a + or - to the representation

chmod +r example.txt

or

chmod -rwx example

Keep in mind that chmod 400 means that the only the owner can read the file, the group and other users do not have any access on the file.

Chmod 0777

To set permissions for a file or directory to 0777, you would use the following command:

chmod 0777 /path/to/file

This would give the owner, group, and others read, write, and execute permissions for the file located at “/path/to/file”.

It’s important to note that 777 is a very open permission and is not recommended for security reason, as it gives all users full read, write, and execute permissions. It is recommended to assign permissions on a need-to-access basis.

Chmod 664

To set permissions for a file or directory to 664, you would use the following command:

chmod 664 /path/to/file

This would give the owner read and write permissions, and the group and others read permissions for the file located at “/path/to/file”.

For example, if you want to change the permissions of all files in a directory, you can use the chmod command in combination with the find command like this:

find /path/to/directory -type f -exec chmod 664 {} \;

It’s important to note that 664 is common permission setup to give read and write access to the owner, and read access to the group and others. It’s a way to make sure the user can modify their own file, while allowing others to read it.

Chmod 0755

To set permissions for a file or directory to 0755, you would use the following command:

chmod 0755 /path/to/file

This would give the owner read, write, and execute permissions, and the group and others read and execute permissions for the file located at “/path/to/file”.

For example, if you want to change the permissions of a directory and all its contents, you can use the chmod command in combination with the -R (recursive) option like this:

chmod -R 0755 /path/to/directory

It’s important to note that 755 is a common permission setup for directories, giving read, write, and execute access to the owner and read and execute access to others and group members. This allows the owner to navigate, create and modify content, but others can only navigate and execute files, such as scripts.

Chmod 444

The command chmod 444 is used to change the permissions on a file or directory, so that the owner has read-only permissions, and all others (group and others) have no permissions.

For example, if you have a file called “example.txt” and you want to make it read-only for everyone, you would run the command:

chmod 444 example.txt

This command changes the permissions on the file “example.txt” so that the owner has read and execute permissions (4), and all others have no permissions (0).

It is a numeric format, every digit represent different permissions, first digit is owner permission, second is group permission, third is others permission, where 0 means no permission, 1 execute, 2 write, 4 read.

Chmod 555

The command chmod 555 is used to change the permissions on a file or directory, so that all users (owner, group, and others) have read and execute permissions, but do not have write permissions.

For example, if you have a file called “example.txt” and you want to make it readable and executable for everyone, but not writable, you would run the command:

chmod 555 example.txt

This command changes the permissions on the file “example.txt” so that the owner, group, and others all have read and execute permissions (5), but do not have write permission (0).

It is a numeric format, every digit represent different permissions, first digit is owner permission, second is group permission, third is others permission, where 0 means no permission, 1 execute, 2 write, 4 read.

Chmod 4755

The command chmod 4755 is used to change the permissions on a file or directory, so that the owner has read, write, and execute permissions, group and others have only execute permission, and the execute bit is set for the file, meaning it will be treated as an executable or a script.

For example, if you have a file called “example.sh” and you want to make it executable and owned by a specific user or group, you would run the command:

chmod 4755 example.sh

This command changes the permissions on the file “example.sh” so that the owner has read, write, and execute permissions (4+2+1=7), group and others have only execute permissions (1) and the file will be treated as an executable. This is also known as the setuid/setgid bit.

It is a numeric format, every digit represent different permissions, first digit is owner permission, second is group permission, third is others permission, where 0 means no permission, 1 execute, 2 write, 4 read.

This command is useful when you want to run a script with the permissions of the owner of the file, regardless of the user who is executing it. It can be useful, but also can be a security risk if not used carefully, as it allows anyone to run the script with owner’s privileges.

Chmod 0600

The command chmod 0600 is used to change the permissions on a file or directory, so that the owner has read and write permissions, and all others have no permissions.

For example, if you have a file called “secret.txt” and you want to make it so that only the owner can read and write to it, you would run the command:

chmod 0600 secret.txt

This command changes the permissions on the file “secret.txt” so that the owner has read and write permissions (6), and all others have no permissions (0). This means that only the owner can read and write to the file, and no one else can access it.

It is a numeric format, every digit represent different permissions, first digit is owner permission, second is group permission, third is others permission, where 0 means no permission, 1 execute, 2 write, 4 read.

This command is useful to restrict access to a file that contains sensitive information. Using the octal values to set permissions, using chmod command , can quickly and easily set more complex permissions.

Chmod 7777

chmod 7777 is a command used in Linux and Unix-based operating systems to change the permissions of a file or directory. It sets the file or directory’s permissions so that the owner has read, write, and execute permissions; the group has read, write, and execute permissions; and all others have read, write, and execute permissions. Here are some examples of how chmod 7777 can be used:

  1. To give full permissions to a file named file.txt:
Copy codechmod 7777 file.txt
  1. To give full permissions to a directory named documents:
chmod -R 7777 documents/

It is important to consider security while use chmod 7777 as it give all the permissions to all users include others as well which can be vulnerable.

Please note that chmod 7777 is not recommended in general, as it gives full permissions to everyone, including non-trusted users and programs. This can be a security risk.

Chmod 2700

chmod 2700 is a command used in Linux and Unix-based operating systems to change the permissions of a file or directory. It sets the file or directory’s permissions so that the owner has full permissions (rwx), the group has no permissions (—) and others also have no permissions (—)

Here are some examples of how chmod 2700 can be used:

  1. To give full permissions to owner and no permission to others and group for a file named file.txt:
chmod 2700 file.txt
  1. To give full permissions to owner and no permission to others and group for a directory named documents:
chmod -R 2700 documents/

It could be useful in situations where you want to protect sensitive data to be shared only with the owner of the file and no others or group members.

It is important to consider that this command gives no permissions to group and others over the directory or file which may or may not be ideal in every situations.

Chmod 2755

chmod 2755 is a command used in Linux and Unix-based operating systems to change the permissions of a file or directory. It sets the file or directory’s permissions so that the owner has full permissions (rwx), the group has execute permission (–x) and others also have execute permission (–x)

Here are some examples of how chmod 2755 can be used:

  1. To give full permissions to owner, execute permission to group and others for a file named file.txt:
chmod 2755 file.txt
  1. To give full permissions to owner, execute permission to group and others for a directory named documents:
chmod -R 2755 documents/

This command is useful in situations where you want to give the execute permission to a group or others for a file or directory but not allow them to read or write the file or access to the directory.

It is important to consider the security implications of giving execute permissions to group or others, as it could make it possible for them to execute malicious scripts or code that could compromise the security of the system.

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