Understanding File Permissions
Linux file systems are permission-driven, which means that improper permissions can prevent GHex or any editor from saving changes to firmware files. Make sure the working file has the correct ownership and permissions.
Use the following command to check file permissions:
```bash
ls -lh path/to/firmware_file
```
To change ownership for your user, run:
```bash
sudo chown your_username:your_groupname path/to/firmware_file
```
Modify permissions to ensure write access:
```bash
chmod u+w path/to/firmware_file
```
Backup the Original Firmware
Before making any modifications, it's prudent to back up the original firmware file to avoid data loss.
Editing with GHex
When using GHex for firmware editing, be aware of how hexadecimal editors manipulate binary data. Any incorrect changes can corrupt the file, so double-check your modifications.
Save As a New File
If saving directly is problematic, try saving your edits as a new file.
After editing in GHex, use the "Save As" feature to save under a different name or directory.
Ensure that the destination directory permits file creation:
```bash
mkdir -p new/directory/path
sudo chmod a+w new/directory/path
```
Validate Edited Firmware
After saving, verify the integrity of the firmware to ensure it isn't corrupted.
Consider using a checksum tool, like md5sum or sha256sum, to compare the original and modified files:
```bash
md5sum path/to/firmware_file
md5sum path/to/edited_firmware_file
```
Restoration and Error Handling
If errors occur, knowing how to revert to the previous working state is important.
Restore the backup file if needed:
```bash
cp path/to/firmware_file.bak path/to/firmware_file
```
If GHex crashes, use backup tools or examine logs (e.g., /var/log/syslog) to identify issues.
Utilize Version Control
For extensive or repeated firmware edits, consider implementing version control (like Git) to track changes and easily revert to working versions.
Initialize a Git repository:
```bash
git init
git add path/to/firmware_file
git commit -m "Initial firmware version"
```
Use branching and commits to manage modifications.
