The Services Router is delivered with the JUNOS Internet software preinstalled. To upgrade the software, you use the J-Web interface or CLI commands to copy a set of software images over the network to memory storage on the Routing Engine.
All junos-jseries software is delivered in signed packages that contain Secure Hash Algorithm 1 (SHA-1) checksums. A package is installed only if the SHA-1 checksum within it matches the SHA-1 hash recorded in its corresponding .sha1 file. (For example, -export.tgz contains -export.tgz and -export.tgz.sha1. The junos-jseries-release-export.tgz package is installed only if the SHA-1 hashes match in the two -export.tgz.sha1 files.)
The junos-jseries package completely reinstalls the software. This package rebuilds the file system but retains configuration files, log files, and similar information from the previous version.