Recovering from File and Directory Permission Errors

Commands often generate error messages because of permission restrictions that are not obvious permission problems; for example, you may get a message similar to Unable to execute command or Could not access file.

In general, you should have read permission for the file you use as input, write permission for the file you enter information in, and execute permission for the command you use. Some commands can be run only by the root user. See the following to recover from file and directory permission errors:

• Checking Files for Read and Write Permissions
• Checking the Command for Execute Permission

If you cannot find the solution to your problem in these articles, return to "Recovering from Software Errors ".

Checking Files for Read and Write Permissions

To recover from read and write permission errors, do the following:

• Determine the current ownership of the file or directory by entering ls -dl Name. You can also enter ls -al without specifying a name to display all files and directories in your current working directory.

  Output similar to the following is displayed for each file or directory specified:

  -rwxr-xr-x  1 root  system   26 Sept 25 12:57 this_one

  -rwxr-xr-x	Specifies the access permissions to the file or directory. The hyphen in the first position indicates that this is a file. A d would indicate a directory. The 2nd, 3rd, and 4th characters, rwx, indicate that the owner has read, write, and execute permissions. The 5th, 6th, and 7th characters, r-x, indicate read and execute permissions for group members. The 8th, 9th, and 10th characters, r-x, indicate read and execute permissions for all others.
  root	Indicates the user that owns the directory.
  system	Indicates the group associated with the directory. In this example, the system group is associated with this file.
  this_one	Specifies the file or directory name.

• Use the following procedures to recover from read and write permission errors.
  1. Run the following command, where the FileName parameter is the name of the file you want to check:

     ls -l FileName

  2. If the command generates an error message, the file does not exist in that directory.
  3. If the command returns the file name and related information, check whether you have read and execute permission.
  4. To add read permission on the file or directory, enter the chmod +r Name command. If you do cannot change read permissions, use the su command to change to the root user or to the owner of the file or directory, and reenter the chmod +r Name.

     OR

     To add write permission on the file or directory, enter the chmod +w Name command. If you cannot change write permission, use the su command to change to the root user or to the owner of the file or directory, and reenter chmod +w Name.

     OR

     Ask the owner of the file or directory to use the chmod command to give you read and/or write permission.

     Note: You can also specify numeric arguments with the chmod command to set permissions on a file or directory for individual groups or users. For example, the chmod 777 Name command enables all permissions on a file or directory. See the "Numeric or Absolute Mode" section in the chmod command for more information.

If you cannot find the solution to your problem in these articles, return to "Recovering from Software Errors".

Checking the Command for Execute Permission

To locate the command and check it for execute permissions, do the following:

1. Find the file where the command resides (whereis Command or the which Command).
2. Run the ls -l command to check the command. The -l flag displays the long version of the listing, including permissions and owner.
3. Check the command for permissions and links to another command. Linked commands are displayed as a second path name.
4. If the command is linked to another command, check that command for permissions also.
5. If you do not have execute permission for the command, or if you do not know how to check the permissions, enter chmod +x Name to add execute permission on the file or directory.

   OR

   If you cannot change execute permission, use the su command to change to the root user or to the owner of the file or directory, and reenter chmod +x Name.

   OR

   Ask the owner of the file or directory to use the chmod command to provide you with execute permission.

   Note: You can also specify numeric arguments with the chmod command to set permissions on a file or directory for individual groups or users. For example, the chmod 777 Name command enables all permissions on a file or directory. See the "Numeric or Absolute Mode" section in the chmod command for more information.

If you cannot find the solution to your problem in these articles, return to "Recovering from Software Errors".