Ne peut pas mettre à jour ubuntu, impossible de télécharger les fichiers

Je suis en train d'essayer :

sudo apt-get update

et j'obtiens :

ravit@ubuntu:/$ sudo apt-get update
Ign http://extras.ubuntu.com trusty InRelease
Ign http://ppa.launchpad.net trusty InRelease                                  
Get:1 http://extras.ubuntu.com trusty Release.gpg [72 B]                       
Get:2 http://extras.ubuntu.com trusty Release [11.9 kB]                        
Ign http://ppa.launchpad.net trusty InRelease                                  
Get:3 http://extras.ubuntu.com trusty/main Sources [14 B]                      
Ign http://us.archive.ubuntu.com trusty InRelease                     
Ign http://security.ubuntu.com trusty-security InRelease              
Ign http://ppa.launchpad.net trusty Release.gpg                       
Get:4 http://security.ubuntu.com trusty-security Release.gpg [933 B]           
Get:5 http://extras.ubuntu.com trusty/main i386 Packages [14 B]                
Get:6 http://security.ubuntu.com trusty-security Release [63.5 kB]             
Ign http://ppa.launchpad.net trusty Release.gpg                                
Get:7 http://security.ubuntu.com trusty-security/main Sources [87.4 kB]        
Ign http://us.archive.ubuntu.com trusty-updates InRelease                      
Ign http://ppa.launchpad.net trusty Release                                    
Get:8 http://security.ubuntu.com trusty-security/restricted Sources [2,061 B]  
Get:9 http://security.ubuntu.com trusty-security/universe Sources [28.1 kB]    
Ign http://ppa.launchpad.net trusty Release                                    
Get:10 http://security.ubuntu.com trusty-security/multiverse Sources [2,337 B] 
Ign http://us.archive.ubuntu.com trusty-backports InRelease                    
Get:11 http://us.archive.ubuntu.com trusty Release.gpg [72 B]                  
Get:12 http://us.archive.ubuntu.com trusty-updates Release.gpg [933 B]         
Get:13 http://security.ubuntu.com trusty-security/main i386 Packages [290 kB]  
Get:14 http://us.archive.ubuntu.com trusty-backports Release.gpg [933 B]       
Get:15 http://us.archive.ubuntu.com trusty Release [11.9 kB]                   
Get:16 http://us.archive.ubuntu.com trusty-updates Release [63.5 kB]           
Get:17 http://us.archive.ubuntu.com trusty-backports Release [63.5 kB]         
Ign http://extras.ubuntu.com trusty/main Translation-en_US                     
Ign http://extras.ubuntu.com trusty/main Translation-en                        
Get:18 http://us.archive.ubuntu.com trusty/main Sources [14 B]                 
Get:19 http://us.archive.ubuntu.com trusty-updates/main Sources [212 kB]       
Get:20 http://security.ubuntu.com trusty-security/restricted i386 Packages [8,846 B]
Get:21 http://security.ubuntu.com trusty-security/universe i386 Packages [111 kB]
Get:22 http://security.ubuntu.com trusty-security/multiverse i386 Packages [3,854 B]
Get:23 http://us.archive.ubuntu.com trusty-updates/restricted Sources [3,433 B]
Get:24 http://security.ubuntu.com trusty-security/main Translation-en [159 kB] 
Get:25 http://us.archive.ubuntu.com trusty-updates/universe Sources [123 kB]   
Err http://ppa.launchpad.net trusty/main i386 Packages                         
  404  Not Found
Ign http://ppa.launchpad.net trusty/main Translation-en_US                     
Ign http://ppa.launchpad.net trusty/main Translation-en                        
Err http://ppa.launchpad.net trusty/main i386 Packages                         
  404  Not Found
Get:26 http://us.archive.ubuntu.com trusty-updates/multiverse Sources [5,151 B]
Get:27 http://security.ubuntu.com trusty-security/multiverse Translation-en [1,679 B]
Get:28 http://security.ubuntu.com trusty-security/restricted Translation-en [2,266 B]
Get:29 http://security.ubuntu.com trusty-security/universe Translation-en [64.0 kB]
Ign http://ppa.launchpad.net trusty/main Translation-en_US                     
Get:30 http://us.archive.ubuntu.com trusty-updates/main i386 Packages [548 kB] 
Ign http://ppa.launchpad.net trusty/main Translation-en                        
Get:31 http://us.archive.ubuntu.com trusty-updates/restricted i386 Packages [11.8 kB]
Get:32 http://us.archive.ubuntu.com trusty-updates/universe i386 Packages [292 kB]
Get:33 http://us.archive.ubuntu.com trusty-updates/multiverse i386 Packages [12.1 kB]
Get:34 http://us.archive.ubuntu.com trusty-updates/main Translation-en [271 kB]
Get:35 http://us.archive.ubuntu.com trusty-updates/multiverse Translation-en [6,148 B]
Get:36 http://us.archive.ubuntu.com trusty-updates/restricted Translation-en [2,774 B]
Get:37 http://us.archive.ubuntu.com trusty-updates/universe Translation-en [154 kB]
Get:38 http://us.archive.ubuntu.com trusty-backports/main Sources [5,851 B]    
Get:39 http://us.archive.ubuntu.com trusty-backports/restricted Sources [28 B] 
Get:40 http://us.archive.ubuntu.com trusty-backports/universe Sources [28.4 kB]
Get:41 http://us.archive.ubuntu.com trusty-backports/multiverse Sources [1,898 B]
Get:42 http://us.archive.ubuntu.com trusty-backports/main i386 Packages [6,285 B]
Get:43 http://us.archive.ubuntu.com trusty-backports/restricted i386 Packages [28 B]
Get:44 http://us.archive.ubuntu.com trusty-backports/universe i386 Packages [32.6 kB]
Get:45 http://us.archive.ubuntu.com trusty-backports/multiverse i386 Packages [1,552 B]
Get:46 http://us.archive.ubuntu.com trusty-backports/main Translation-en [3,645 B]
Get:47 http://us.archive.ubuntu.com trusty-backports/multiverse Translation-en [1,215 B]
Get:48 http://us.archive.ubuntu.com trusty-backports/restricted Translation-en [14 B]
Get:49 http://us.archive.ubuntu.com trusty-backports/universe Translation-en [29.6 kB]
Fetched 2,731 kB in 11s (242 kB/s)                                             
W: Failed to fetch http://ppa.launchpad.net/octave/stable/ubuntu/dists/trusty/main/binary-i386/Packages  404  Not Found

W: Failed to fetch http://ppa.launchpad.net/picaso/octave/ubuntu/dists/trusty/main/binary-i386/Packages  404  Not Found

W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty/Release  Unable to find expected entry 'restricted/source/Sources' in Release file (Wrong sources.list entry or malformed file)

E: Certains index des fichiers n'ont pas pu être téléchargés. Ils ont été ignorés, ou les anciens ont été utilisés à la place.

Quel est le problème ? (j'utilise Ubuntu DISTRIB_RELEASE=14.04)