udev rule works with command echo but not with cp command

Question about a `udev` rule that works with the `echo` command but not with the `cp` command. If you're encountering a similar issue with your `udev` rule, it could be related to environment variables and permissions. Here are some steps to help troubleshoot and resolve the problem:


1. **Check Permissions**:

   - Ensure that the `udev` rule has the necessary permissions to execute the `cp` command. Make sure that the rule's owner, group, and permissions are set correctly. You can use the `ls -l` command to inspect the rule file's permissions.


2. **Specify Full Paths**:

   - In your `udev` rule, specify the full path to the `cp` command. The rule might not be able to locate the `cp` command if the environment variables are not fully set. For example, use `/bin/cp` instead of just `cp`.


3. **Environment Variables**:

   - Environment variables like `PATH` might not be fully set when `udev` runs, and this can affect the execution of some commands. If specifying the full path doesn't work, you might need to set the `PATH` explicitly in your `udev` rule.


   ```udev

   ENV{ID_VENDOR}=="ABC", ACTION=="add", RUN+="/bin/sh -c 'PATH=/bin:/sbin:/usr/bin cp ...'"

   ```


4. **Use a Script**:

   - Instead of running the `cp` command directly in the `udev` rule, create a small script that performs the copy operation and call that script in your rule. This provides better control over environment variables and paths.


   ```udev

   ENV{ID_VENDOR}=="ABC", ACTION=="add", RUN+="/bin/sh -c '/path/to/your/script.sh'"

   ```


5. **Redirect Output and Errors**:

   - When the `udev` rule doesn't behave as expected, it can be helpful to redirect both standard output and errors to a file to capture any error messages or debug information. This can be useful for diagnosing issues.


   ```udev

   ENV{ID_VENDOR}=="ABC", ACTION=="add", RUN+="/bin/cp ... > /path/to/logfile 2>&1"

   ```


6. **Check for AppArmor/SELinux Restrictions**:

   - If you're using AppArmor or SELinux, these security frameworks might restrict the actions of the `udev` rule. Check their logs or policies for any denials.


7. **Debugging Output**:

   - Add debugging output to your `udev` rule. Use commands like `echo` to print messages and variables to a log file or console to help diagnose issues.


Remember that `udev` rules can run with a limited environment, so explicitly specifying paths and controlling environment variables are often necessary. If you're still encountering problems after following these steps, examining error messages and logs can help pinpoint the issue more precisely.

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