Err http://mirrors.digitalocean.com/ubuntu/ precise-security/main libnss3 amd64 3.14.3-0ubuntu0.12.04.1 404 Not Found [IP: 198.199.99.226 80] Fetched 1,757 kB in 0s (10.8 MB/s) Failed to fetch http://mirrors.digitalocean.com/ubuntu/pool/main/n/nspr/libnspr4_4.9.5-0ubuntu0.12.04.1_amd64.deb 404 Not Found [IP: 198.199.99.226 80] Failed to fetch http://mirrors.digitalocean.com/ubuntu/pool/main/n/nss/libnss3_3.14.3-0ubuntu0.12.04.1_amd64.deb 404 Not Found [IP: 198.199.99.226 80] E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing? when i install gcc ,it throw the error