# gfc-file compare

### File and Disk cloning, benchmark, compare and hash utility
☂︎ Optimised for high performance and low CPU usage  
☂︎ Locks disks for exclusive access while cloning  
☂︎ Allows access to protected files bypassing security ACL  

#### Command line options

| Argument                  | `gfc <file1> [file2] [-##]` |
| :------------------------ | :-------------------------- |
| `-b -bench`               | Benchmark read or write, also disables hash processing |
| `-l -log`                 | Use with `-b` or `-B` for benchmark write to `gfc-log.txt` |
| `-l -b`                   | Benchmark write 0x00 to `gfc-log.txt` |
| `-l -B`                   | Benchmark write 0xff to `gfc-log.txt` |
| `-q -quiet`               | Suppress messages to STDOUT, use when writing to STDOUT |
| `-v -verbose`             | Output more debug messages to STDOUT |
| `-md2 -md4 -md5 -sha1`    | Calculate hash using: MD2 MD4 MD5 SHA1 |
| `-sha256 -sha384 -sha512` | Calculate hash using: SHA256 SHA384 SHA512 |
| `-c -compare`             | Compare the entire file content: by default, the program displays |
|                           | only the first difference and exits. |
| | |
| `-p -peak`                | Calculate peaks for 16 bit RAW audio files |
| `-n -normalize`           | Normalise level for 16 bit RAW audio files |
| `-t`                      | Try to assign each thread on it's own processor |
| `-L -lock -dismount`      | Lock and dismount volumes or partitions (works only on Windows) |
|                           | This asserts exclusive access and is important when clonning. |
|                           | Linux: please umount all volumes manually, before accessing |
|                           | a disk or partition. |
| | |
| `-O -offline`             | Take disks offline (works only on Windows) |
|                           | This asserts exclusive access and is important when clonning. |
|                           | On Linux this notifies the system to scan the disk for changes |
|                           | to the partition table, when the program exits. |
| | |
| `-OO`                     | Implies `-O`. Leave disks offline when the operation is complete: |
|                           | It is safe to detach any offline disk as soon as the program exits. |
|                           | If all attached disks are offline, it is also safe to cut power to |
|                           | the computer. Otherwise, use the shutdown command. |
|                           | Warning: | 
|                           | Since cloning creates an exact copy, a clonned disk has the same |
|                           | GUID as the source. It is important to never have two disks with |
|                           | the same GUID attached and online at the same time. Otherwise the |
|                           | system will change the GUID on one of the disks, which prevents |
|                           | any system boot volume on it from being detected. Any operating |
|                           | system on that disk will be left in a non-operational state, since |
|                           | it does not know which volume contains its files. This state can |
|                           | be recovered by editing the Windows registry: Boot the computer to |
|                           | a working installation or Windows setup. Note the drive letter of |
|                           | the system that needs to be recovered: e.g. `D:` |
|                           | Start `regedit`, `File`, `Load hive`: |
|                           | `D:\Windows\System32\config\SYSTEM` as `sys`. |
|                           | Navigate to `HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices`. |
|                           | Edit `\DosDevices\D:`, and copy the hex data. |
|                           | Navigate to `HKEY_LOCAL_MACHINE\sys\MountedDevices`. |
|                           | Edit `\DosDevices\C:`, and replace the hex data with the copy from |
|                           | the previous step. The system should now boot correctly. |
| | |
| `-Write`                  | Copy `file1` to `file2`. Without this, a copmpare is performed. |
| `-a -append`              | `file1` is appended at the end of `file2` |
| `-r -resume`              | Resume an interrupted copy. Implies `-append`. |
| `-[0-9][0-9]`             | Set number of buffers and page size, for example: |
| `-4#`                     | Set `number_of_buffers = 1 << 4 = 16` |
|                           | Higher values minimize the effect of disk speed variation |
| | |
| `-#5`                     | Set `page_size = 2MB << 5 = 64 MB` |
|                           | When accessing two files on the same disk, a value of 5 should |
|                           | reduce the seek overhead and improve performance on spinning disks. |
| | |
| `-P[0-9]`                 | Set `page_size = 512 << 0..9`, allows setting a small page size: |
|                           | this could be very slow, but is useful when there is physical damage |
|                           | to the media. Since unreadable blocks are skipped, setting this to |
|                           | the sector size of the disk allows as much data as possible to be |
|                           | recovered. Note that the default page size is 2 MB, so a deffective |
|                           | sector of 512 bytes would cause the entire page to be skipped. |


###### Example: Compare disk against `image.img` and calculate `SHA256` hash
```powershell
gfc /dev/sdb image.img -sha256              # Linux
gfc \\.\PhysicalDrive0 image.img -sha256    # Windows
```

###### Example: Compare volume against `image.img` on Linux
```powershell
gfc /dev/sdb1 image.img
gfc /dev/disk/by-path/acpi-VMBUS:00-scsi-0:0:0:0 image.img
gfc /dev/disk/by-path/acpi-VMBUS:00-scsi-0:0:0:0-part1 image.img
gfc /dev/disk/by-partlabel/gvalkov image.img
```

###### Example: Compare volume against `image.img` on Windows
```powershell
gfc \\.\d: image.img -md5
gfc \\.\globalroot\Device\Harddisk0\Partition1 image.img
gfc \\.\globalroot\Device\HarddiskVolume1 image.img
gfc \\.\Harddisk0Partition1 image.img
```

###### Example: Compress volume to `d.img.7z` and calculate `SHA1` hash:
Use `-` or `con` as file name to read from `STDIN` or write to `STDOUT`.
```powershell
gfc /dev/sdb1 - -Write -L -sha1 | 7z a -si -m0=LZMA2 -mx=7 -md=32m -mfb=128 d.img.7z
gfc \\.\d:    - -Write -L -sha1 | 7z a -si -m0=LZMA2 -mx=7 -md=32m -mfb=128 d.img.7z
```

###### Example: Restore volume from `d.img.7z` and calculate `SHA1` hash:
```powershell
7z x -so d.img.7z | gfc - /dev/sdb1 -Write -L -sha1   # Linux
7z x -so d.img.7z | gfc - \\.\d:    -Write -L -sha1   # Windows
```

###### Miscelaneous examples
```powershell
gfc file.txt:stream1 -sha1  # sha1 hash for stream1 in file.txt
gfc image.img	            # creates hash of [image.img], SHA1 is the default hash algorithm
gfc -b -l                   # benchmark write performance 0x00 to [gfc-log.txt]
gfc -B -l                   # benchmark write performance 0xFF to [gfc-log.txt]
gfc \\.\d: -Write -L -b -l  # destroy data on vol [\\.\d:]
gfc src.raw dst.raw -n      # performs peak level audio normalization
```

This tool can utilise large memory page support to improve performance.
The feature requires Windows 2003 or later, and the user must have the
`Lock pages in memory` priviledge, which can be set in
`Local Security Policy`, `Local Policies`, `User Rights Assignment`.


#### Supported Platforms
☂︎ Apple iOS, macOS  
☂︎ FreeBSD  
☂︎ Linux, OpenWRT  
☂︎ Windows  


#### [Prerequisites and build instructions](../../../lib.git#Prerequisites)


#### © 2008-2023 Georgi Valkov
https://httpstorm.com/download/gfc-file-compare/