Resume Downloads with curl

Resuming downloads with curl

If you’re on an unstable WiFi hotspot or simply forgot about a curl download and shut down your laptop, there’s a really cool thing to try: resume download from where you left off.

How To Download a File with curl

I’m downloading the Solus 4.1 release – it’s a 1.7GB ISO image. Here’s the command line that makes curl download the file and put it into local file (note the -O option):

greys@xps:~/Downloads/try $ curl -O http://solus.veatnet.de/iso/images/4.1/Solus-4.1-Budgie.iso  

How To Stop Download with curl

Now, if we press Ctlr+C to stop download, we’ll end up with a partially downloaded file:

greys@xps:~/Downloads $ curl -O http://solus.veatnet.de/iso/images/4.1/Solus-4.1-Budgie.iso
   % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current                                         
                                  Dload  Upload   Total   Spent    Left  Speed                                           
   3 1692M    3 58.8M    0     0  2161k      0  0:13:21  0:00:27  0:12:54 4638k^C  

greys@xps:~/Downloads $ ls -la Solus*iso
-rw-r--r-- 1 greys 102318080 Feb 7 22:58 Solus-4.1-Budgie.iso
greys@xps:~/Downloads $ du -sh Solus-4.1-Budgie.iso
98M Solus-4.1-Budgie.iso

How To Resume Download with curl

To resume download (rather than restart and begin downloading the whole file again0, simply use the -C option. It’s meant to be taking a specific offset in bytes, but also works if you specify “-“, when curl looks at existing file and decides what the offset should be automatically:

That’s it, you can let the download complete now:

greys@xps:~/Downloads $ curl -C - -O http://solus.veatnet.de/iso/images/4.1/Solus-4.1-Budgie.iso                        

** Resuming transfer from byte position 102318080                                                                       

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current                                         

                                 Dload  Upload   Total   Spent    Left  Speed                                           

100 1595M  100 1595M    0     0  2868k      0  0:09:29  0:09:29 --:--:-- 1766k         

Here’s my resulting file:

-rw-r--r-- 1 greys 1774911488 Feb  7 23:08 Solus-4.1-Budgie.iso

Don’t Forget to Compare File Checksum!

Checking a checksum for newly downloaded ISO image is always a good practice, but it becomes a must when you’re resuming downloads: in addition to ensuring you got the same ISO image software distributors intended, you’re getting the assurance that your resumed download file is intact and fully operational.

I have downloaded Solus 4.1 SHA256 checksum from the same Solus Downloads page, and will use the sha256sum command to generate checksum for the ISO file. Obviously, both checksums must match:

greys@xps:~/Downloads $ cat Solus-4.1-Budgie.iso.sha256sum 
4bf00f2f50e7024a71058c50c24a5706f9c18f618c013b8a819db33482577d17  Solus-4.1-Budgie.iso
greys@xps:~/Downloads $ sha256sum Solus-4.1-Budgie.iso
4bf00f2f50e7024a71058c50c24a5706f9c18f618c013b8a819db33482577d17  Solus-4.1-Budgie.iso

That’s it for today! I can’t wait to try Solus 4.1, will posh about it shortly.

See Also