On Sat, Jan 24, 2026 at 07:01:00PM -0700, Tom Dial wrote: > > > On 1/24/26 07:33, Greg Wooledge wrote: > > On Sat, Jan 24, 2026 at 16:09:12 +0500, Alexander V. Makartsev wrote: > > > "cp -r /dev/ /tmp/RFS/dev/" is wrong! Don't do that. > > > Think about it, "cp" command will copy block devices such as /dev/sda like > > > files into /tmp/RFS, basically into itself until it runs out of free > > > space. > > > > I remember, a number of years ago, getting caught by exactly this, I believe > on an earlier version of Debian. > > Considering that things might have changed since then, I tried it, with the > following results: > > root@dyson:~# mkdir /mnt/test > root@dyson:~# cp /dev/sda1 /mnt/test > root@dyson:~# du /mnt/test > 173870 /mnt/test > root@dyson:~# ll /mnt/test > total 173861 > -rw-r----- 1 root root 535822336 Jan 24 18:22 sda1 > root@dyson:~# ll /mnt/test/sda1 > -rw-r----- 1 root root 535822336 Jan 24 18:22 /mnt/test/sda1
[...] This behaviour doesn't apply when -r option is given. Then, special files are copied as such *unless* you give option --copy-contents. It's all in the docs, but... tomas@caliban:~$ mkdir /tmp/foo tomas@caliban:~$ sudo cp -r /dev/sda1 /tmp/foo [sudo] password for tomas: tomas@caliban:~$ ls -al /tmp/foo total 20 drwxr-xr-x 2 tomas tomas 4096 Jan 25 09:39 . drwxrwxrwt 9 root root 16384 Jan 25 09:39 .. brw-r----- 1 root root 8, 1 Jan 25 09:39 sda1 The problem with -r is that it misses other (important) file attributes, as has been said elsewhere in this thread. Still, bind mount is the better option. Back then, long, long time ago, cp was the only available, so those recipes still float around in the intrawebs, like ghost ships. Harr! Cheers -- t
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