Copy (synchronize) remote folder to local over ssh:
rsync -avzhe ssh --progress user@server:~/folder .
Copy (synchronize) local folder to remote over ssh:
rsync -avzhe ssh --progress /folder user@server:~/folder
If your destination directory has some files which are not in source, by default they will remain. Use --delete option to delete them at the destination directory also. Following command will copy files from remote to local, making sure to delete local files which are not on remote:
rsync -avzhe ssh --progress --delete user@server:~/folder .
You can always add a dry run option --dry-run which will output results without actually copying anything.
You can also syncrhonize local folder with another local folder:
rsync -av --delete ~/folder1/ ~/folder2/
Specifying / after the source directory only copies the contents of the directory. If we do not specify the / the source directory, the source directory will also be copied to the destination directory.
-a specifies the archive mode, meaning you want recursion and you want to preserve almost everything
-v specifies verbosity
First, check and mount the usb drive, main partition (/dev/sdX3) to /mnt and boot partition (/dev/sdX2/) to /mnt/boot:
lsblk
sudo mount /dev/sdX3 /mnt
sudo mkdir /mnt/boot
sudo mount /dev/sdX2 /mnt/boot
Then, copy the whole root partition to USB with rsync, in archive mode but excluding some machine-specific directories, including /etc/fstab and /boot:
sudo rsync -aAXv --exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*","/lost+found","/etc/fstab","/boot/*"} --delete / /mnt/
When you are rsynching from the USB drive to your local Arch installation, just reverse the source and destination folder, from / /mnt/ to /mnt/ /.
In case there are some changes to /boot folder, for example after a kernel upgrade, you must not exclude the /boot folder! Run the following rsync command instead:
sudo rsync -aAXv --exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*","/lost+found","/etc/fstab"} --delete / /mnt/
In addition, you have to run following commands so that the boot configuration is rebuilt on the USB drive:
arch-chroot /mnt mkinitcpio -p linux
arch-chroot /mnt grub-mkconfig -o /boot/grub/grub.cfg
In case you have Arch Linux LTS kernel installed (check with uname -r) use linux-lts instead of linux in the above mkinitcpio command!
You can now unmount the USB drive. When you boot from it, it should boot to the equivalent system!
sudo umount /mnt/boot /mnt