I install QGIS 2.8 in debian (linux) through nightly jessie (qgis testing) and I see that SAGA is not in processing toolbox, so I install saga gis software but still it doesn't appear in processing.
How do I run SAGA in processing toolbox?
UPDATE:
This problem is resolved through the line commands:
sudo add-apt-repository ppa:johanvdw/saga-gis
sudo apt-get update
sudo apt-get install saga
But in my case (Debian Jessie) instead of sudo add-apt-repository ppa:johanvdw/saga-gis I went to https://launchpad.net/~johanvdw/+archive/ubuntu/saga-gis and in Technical details about this PPA I choose Trusty version, copy the lines and paste in sources.list. It works!!!
I try the commands in terminal but it didn't work and I get this error (I suppose it is not correct):
sudo apt-get update
Hit http://ftp.pt.debian.org jessie InRelease
Hit http://ftp.pt.debian.org jessie-updates InRelease
Hit http://ftp.pt.debian.org jessie-backports InRelease
Ign http://ppa.launchpad.net jessie InRelease
Hit http://security.debian.org jessie/updates InRelease
Ign http://ppa.launchpad.net jessie InRelease
Ign http://ppa.launchpad.net jessie InRelease
Get:1 http://ftp.pt.debian.org jessie/main Sources/DiffIndex [7,876 B]
Ign http://ppa.launchpad.net jessie InRelease
Get:2 http://qgis.org sid InRelease [3,341 B]
Ign http://ppa.launchpad.net jessie InRelease
Ign http://ppa.launchpad.net jessie InRelease
Ign http://ppa.launchpad.net jessie InRelease
Ign http://ppa.launchpad.net jessie Release.gpg
Ign http://ppa.launchpad.net jessie Release.gpg
Ign http://ppa.launchpad.net jessie Release.gpg
Get:3 http://ftp.pt.debian.org jessie/main amd64 Packages/DiffIndex [7,876 B]
Get:4 http://ftp.pt.debian.org jessie/main Translation-en/DiffIndex [7,876 B]
Ign http://ppa.launchpad.net jessie Release.gpg
Ign http://ppa.launchpad.net jessie Release.gpg
Ign http://ppa.launchpad.net jessie Release.gpg
Ign http://ppa.launchpad.net jessie Release.gpg
Ign http://ppa.launchpad.net jessie Release
Ign http://ppa.launchpad.net jessie Release
Ign http://ppa.launchpad.net jessie Release
Ign http://ppa.launchpad.net jessie Release
Hit http://ftp.pt.debian.org jessie-updates/main Sources
Ign http://qgis.org sid InRelease
Hit http://ftp.pt.debian.org jessie-updates/main amd64 Packages
Hit http://ftp.pt.debian.org jessie-updates/main Translation-en
Hit http://ftp.pt.debian.org jessie-backports/main Sources
Hit http://ftp.pt.debian.org jessie-backports/main amd64 Packages
Ign http://ppa.launchpad.net jessie Release
Ign http://ppa.launchpad.net jessie Release
Hit http://ftp.pt.debian.org jessie-backports/main Translation-en
Ign http://ppa.launchpad.net jessie Release
Ign http://qgis.org sid/main Sources/DiffIndex
Hit http://security.debian.org jessie/updates/main Sources
Hit http://security.debian.org jessie/updates/main amd64 Packages
Hit http://security.debian.org jessie/updates/main Translation-en
Ign http://qgis.org sid/main amd64 Packages/DiffIndex
Hit http://qgis.org sid/main amd64 Packages
Ign http://qgis.org sid/main Translation-en_US
Err http://ppa.launchpad.net jessie/main amd64 Packages
404 Not Found
Ign http://ppa.launchpad.net jessie/main Translation-en_US
Ign http://qgis.org sid/main Translation-en
Ign http://ppa.launchpad.net jessie/main Translation-en
Err http://ppa.launchpad.net jessie/main amd64 Packages
404 Not Found
Ign http://ppa.launchpad.net jessie/main Translation-en_US
Ign http://ppa.launchpad.net jessie/main Translation-en
Hit http://qgis.org sid/main Sources
Err http://ppa.launchpad.net jessie/main amd64 Packages
404 Not Found
Ign http://ppa.launchpad.net jessie/main Translation-en_US
Ign http://ppa.launchpad.net jessie/main Translation-en
Err http://ppa.launchpad.net jessie/main amd64 Packages
404 Not Found
Ign http://ppa.launchpad.net jessie/main Translation-en_US
Ign http://ppa.launchpad.net jessie/main Translation-en
Err http://ppa.launchpad.net jessie/main amd64 Packages
404 Not Found
Ign http://ppa.launchpad.net jessie/main Translation-en_US
Ign http://ppa.launchpad.net jessie/main Translation-en
Err http://ppa.launchpad.net jessie/main amd64 Packages
404 Not Found
Ign http://ppa.launchpad.net jessie/main Translation-en_US
Ign http://ppa.launchpad.net jessie/main Translation-en
Err http://ppa.launchpad.net jessie/main amd64 Packages
404 Not Found
Ign http://ppa.launchpad.net jessie/main Translation-en_US
Ign http://ppa.launchpad.net jessie/main Translation-en
Fetched 27.0 kB in 10s (2,690 B/s)
W: GPG error: http://qgis.org sid InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 030561BEDD45F6C3
W: Failed to fetch http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu/dists/jessie/main/binary-amd64/Packages 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/johanvdw/saga-gis/ubuntu/dists/jessie/main/binary-amd64/Packages 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/otb/orfeotoolbox-nightly/ubuntu/dists/jessie/main/binary-amd64/Packages 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/otb/orfeotoolbox-stable/ubuntu/dists/jessie/main/binary-amd64/Packages 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/otb/orfeotoolbox-stable-ubuntugis/ubuntu/dists/jessie/main/binary-amd64/Packages 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/ubuntu-toolchain-r/test/ubuntu/dists/jessie/main/binary-amd64/Packages 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/ubuntugis/ubuntugis-unstable/ubuntu/dists/jessie/main/binary-amd64/Packages 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.
Best Answer
I had the same problem, but, looking on the web, I found a solution. Simply, I installed SAGA from other repository (Installing SAGA GIS 2.1).
Try the following commands from a command line:
I hope it works.