Skip to main content

UNIX: ssh + tar + gzip -q = goodness

To retrieve a hierarchy of files from a remote server (or to copy it back to a remote server), I often do something like:
ssh servername "tar cvzf - dirname" | tar xvfz -
However, I usually get the following error message:
gzip: stdin: decompression OK, trailing garbage ignored
tar: Child returned status 2
tar: Error exit delayed from previous errors
Strangely enough, as I write this, I get the error message copying something from one FreeBSD system to another FreeBSD system, but I don't get it when copying something from one FreeBSD system to my Ubuntu system. Weird.

I put up with this problem for years. However, I recently needed to use it in a Makefile. Having an error like that is fine when you're a human, but a non-zero return code is a deal-breaker in a Makefile. I needed to clean up my act.

One easy way to make the problem go away is to not use the "z" flag for both instances of tar. This is somewhat icky, because it really would be nice to have the content gzipped. Otherwise, it could take too long to transfer.

Finally, I found the real solution on the gzip Web site. Instead of passing the "z" flag to tar when untarring, use gunzip separately and pass the "q" flag to tell it to be quiet:
ssh server "tar cvzf - dirname" | gunzip -q | tar xvf -
By the way, as is standard in UNIX, there are plenty of other variations of this tar + ssh idiom. For instance, consider:
ssh server "cd myapplication/share/locale && 
find . -name '*.po' -o -name '*.mo' |
xargs tar cvzf -" |
gunzip -q | tar xvf -

Comments

Anonymous said…
From Brandon Golm:

do you have anything agains cpio, and letting ssh handle the compression
with '-C' ??

well... your way is good too.
jjinux said…
I can never remember the arguments for cpio ;)

I didn't know about ssh's "-C" argument. That's *even better* (less typing!), although I sure am glad to know the right way to work around my other way.
jjinux said…
ssh -C servername "tar cvf - dirname" | tar xvf -

Yep, worked just fine!
Leon Atkinson said…
I wonder if compression is all that relevant, anyway. Most of the time, I have a fast, unsaturated network between my local machine and any remote machine.
Leon Atkinson said…
OK--I couldn't resist testing. It's relevant for my 768K DSL connection. My crude test showed 1 minute versus 6 minutes.

I wonder if I shouldn't add "Compression yes" to /etc/ssh/ssh_config.
Anonymous said…
Take a look at rsync. :)
Anonymous said…
I don't find cpio all that difficult:
cpio -i means data is coming from stdin,
cpio -o means data is going to stdout.

Also
find directory (-some-complicated-query) | cpio -o
find directory (-some-complicated-query) -print0 | cpio -0o
is easier than
find directory (-some-complicated-query) | xargs -d'\n' tar cf -
find directory (-some-complicated-query) -print0 | xargs -0 tar cf -
(for safety with working with filenames with spaces and other interesting characters)
jjinux said…
> I don't find cpio all that difficult:

+1 for usefulness. I stand corrected!
Unknown said…
your problem here was that you had the "v" option on the sending side of the tar, instead of just on the untar.
ssh user@host "tar czf - dirname " | tar zxvf -
should work fine.
jjinux said…
> your problem here was that you had the "v" option on the sending side of the tar, instead of just on the untar.

Wow, that makes perfect sense! Thanks!

Popular posts from this blog

Drawing Sierpinski's Triangle in Minecraft Using Python

In his keynote at PyCon, Eben Upton, the Executive Director of the Rasberry Pi Foundation, mentioned that not only has Minecraft been ported to the Rasberry Pi, but you can even control it with Python . Since four of my kids are avid Minecraft fans, I figured this might be a good time to teach them to program using Python. So I started yesterday with the goal of programming something cool for Minecraft and then showing it off at the San Francisco Python Meetup in the evening. The first problem that I faced was that I didn't have a Rasberry Pi. You can't hack Minecraft by just installing the Minecraft client. Speaking of which, I didn't have the Minecraft client installed either ;) My kids always play it on their Nexus 7s. I found an open source Minecraft server called Bukkit that "provides the means to extend the popular Minecraft multiplayer server." Then I found a plugin called RaspberryJuice that implements a subset of the Minecraft Pi modding API for B

Ubuntu 20.04 on a 2015 15" MacBook Pro

I decided to give Ubuntu 20.04 a try on my 2015 15" MacBook Pro. I didn't actually install it; I just live booted from a USB thumb drive which was enough to try out everything I wanted. In summary, it's not perfect, and issues with my camera would prevent me from switching, but given the right hardware, I think it's a really viable option. The first thing I wanted to try was what would happen if I plugged in a non-HiDPI screen given that my laptop has a HiDPI screen. Without sub-pixel scaling, whatever scale rate I picked for one screen would apply to the other. However, once I turned on sub-pixel scaling, I was able to pick different scale rates for the internal and external displays. That looked ok. I tried plugging in and unplugging multiple times, and it didn't crash. I doubt it'd work with my Thunderbolt display at work, but it worked fine for my HDMI displays at home. I even plugged it into my TV, and it stuck to the 100% scaling I picked for the othe

Creating Windows 10 Boot Media for a Lenovo Thinkpad T410 Using Only a Mac and a Linux Machine

TL;DR: Giovanni and I struggled trying to get Windows 10 installed on the Lenovo Thinkpad T410. We struggled a lot trying to create the installation media because we only had a Mac and a Linux machine to work with. Everytime we tried to boot the USB thumb drive, it just showed us a blinking cursor. At the end, we finally realized that Windows 10 wasn't supported on this laptop :-/ I've heard that it took Thomas Edison 100 tries to figure out the right material to use as a lightbulb filament. Well, I'm no Thomas Edison, but I thought it might be noteworthy to document our attempts at getting it to boot off a USB thumb drive: Download the ISO. Attempt 1: Use Etcher. Etcher says it doesn't work for Windows. Attempt 2: Use Boot Camp Assistant. It doesn't have that feature anymore. Attempt 3: Use Disk Utility on a Mac. Erase a USB thumb drive: Format: ExFAT Scheme: GUID Partition Map Mount the ISO. Copy everything from