Archive Mode and Friends

Scope: what -a switches on, proof that it works, and the gaps you have to close on purpose.

-a unpacked

Nearly every rsync command in the wild starts with -a. It is a bundle — shorthand for -rlptgoD — and each letter earns its place:

Flag	Name	What it does
-r	recursive	descend into subdirectories
-l	links	copy symlinks as symlinks, not as the files they point to
-p	perms	preserve permission bits
-t	times	preserve modification times
-g	group	preserve group ownership
-o	owner	preserve owner (only meaningful as root / with privilege)
-D	devices + specials	preserve device files and fifos (privileged)

This is the sane default because a synchroniser that quietly resets times and permissions isn't synchronising — it's photocopying, and worse, it breaks the quick check (next chapters) that makes the next run cheap: preserved times are how rsync later knows a file is unchanged.

From the lab, the whole bundle at work in one pass over a tree containing an old file, a private file, an executable, and a symlink:

$ ls -l arch/old.txt arch/secret.txt arch/bin/run.sh
-rwxr-xr-x 1 root root 33 Oct 17 23:47 arch/bin/run.sh
-rw-rw---- 1 root root 20 Jan  2  2020 arch/old.txt
-rw------- 1 root root 31 Oct 17 23:47 arch/secret.txt

$ ls -l arch/link.txt
lrwxrwxrwx 1 root root 10 Oct 17 23:47 arch/link.txt -> README.txt

$ stat -c "%y %n" project/old.txt arch/old.txt
2020-01-02 03:04:00.000000000 +0000 project/old.txt
2020-01-02 03:04:00.000000000 +0000 arch/old.txt

The date on old.txt is from 2020 on both sides, the script is still executable, the private file is still 600, the link is still a link, and an empty directory in the source arrived as an empty directory — plain cp -r folklore gets at least two of those wrong.

Check: after any sync where fidelity matters, ls -l a file whose properties you know on both sides. Times and modes either match or they don't; there's no partial credit to argue about.

The working companions

Option	What it adds
-v	verbose: list what was transferred (repeat as -vv for more)
--progress	per-file progress and speed during big transfers: 31,457,280 100% 275.23MB/s 0:00:00
-h	human-readable sizes in the summaries
-n, --dry-run	show what would happen, change nothing — the subject of the next chapter
--stats	a full report: files transferred, literal vs matched data, totals

What -a deliberately leaves out

Archive mode is a curated default, and three omissions matter:

• Hardlinks are not preserved (-H). Two names for one file in the source become two separate files in the destination — correct contents, doubled disk, and a broken relationship if the two names were meant to stay the same file:

``` $ ls -li arch/data.bin arch/data-copy.bin (plain -a) 5684929 -rw-rw---- 1 root root 18 ... arch/data-copy.bin 5684930 -rw-rw---- 1 root root 18 ... arch/data.bin

$ ls -li archH/data.bin archH/data-copy.bin (with -H) 5684948 -rw-rw---- 2 root root 18 ... archH/data-copy.bin 5684948 -rw-rw---- 2 root root 18 ... archH/data.bin ```

Different inode numbers (first column) mean different files; the same inode, with link count 2, means one file with two names. Add -H whenever the source tree uses hardlinks on purpose — backup trees and snapshot stores do, which is why the backup chapter cares.

• ACLs (-A) and extended attributes (-X) are not preserved (documented). If your files carry access-control lists or xattrs that matter, plain -a drops them silently. Add -A, -X (often -AX) once you've confirmed your destination filesystem supports them.

• Sparse files are not recreated sparsely without --sparse (documented) — a mostly empty disk image can arrive fat. And files are not compared by content: -a trusts the quick check, like everything else in rsync (chapter: How rsync Decides What to Send).

The pattern to remember: -a first, then add the specific letters the tree in front of you needs.