**5.4 Site services**

As mentioned before, there are several AliEn services running at each ALICE site: CE, ClusterMonitor, PackMan and MonALISA. These services are running on a dedicated machine, so-called VOBOX described in section 3.

The AliEn site CE is usually associated with the local batch system. It is periodically submitting testing pilot jobs (Job Agents) to the local WLCG CE or an appropriate external Resource Broker or WMS. The role of the Job Agents is to verify the local hardware and software capacities at the site. After the usual matchmaking procedure, the JA is sent, through the site CE, into the local batch queue and then to a local Worker Node (WN). After its startup, the JA performs its task and in the case of a positive checkup, the JA requests a "real" job from the central Task Queue via the AliEn Job Broker, or dies otherwise. The PackMan automates the process of installation, upgrades, configuration and removal of the ALICE software packages from the shared software area on the site. It also advertises known/installed packages. The packages are installed on demand, when requested by a Job Agent running on a Worker Node or during the central software deployment over the Grid sites. If a package is not already installed the PackMan would install it along with its dependencies and return a string with commands that client has to execute to configure the package and all its dependencies. The PackMan manages the local disk cache and cleans it, when it needs more space to install newer packages. The Cluster Monitor handles communication with the AliEn Job Broker and gives configuration to JAs. It gets "heartbeats" from the JAs. If it gets no heartbeats from a JA, the existing job will get into the ZOMBIE status (after 1.5 hours) and then it will expire (after 3 hours).
