Organization of SINQ Data Acquisition

Client Server Data Acquisition

SINQ uses SICS as its data acquisition program. SICS is a client server system. Thus at any given time at least two programs are required to operate SICS:

1. A SICS client. SICS clients can run on any computer
2. A SICS server. The SICS server runs on the instrument computer.

The two programs communicate with each other through the TCP/IP network and a simple ASCII command protocol.

The Instrument Computer

For each instrument there is an instrument computer. This computer is named like the instrument. For example, for the instrument AMOR the instrument computer is amor.psi.ch. Instrument computers are HP workstations equipped with two disks set up in RAID 1 (mirroring) configuration. For most instruments the instrument computer is located in the instruments cabin. The instrument computers run linux. At the time of writing Scientific Linux 6.

Instrument Computer Accounts

On each instrument computer there are two important local user accounts:

1. The instrument user account
2. The instrument guest account

The instrument account is used to run the SICS server. Its name is the same as the name of the instrument. The password follows a scheme: instrument name + lns, all in capitals. Thus for amor the credentials for this account are: amor/AMORLNS. Ordinary users are not meant to touch this account.

The instrument guest account is named inst + lnsg. The password is the last two digits of the year + lns1. Thus, again for the amor example, the credentials are amorlnsg/14lns1. The instrument guest account supposed to be used by SINQ users and holds user data such as batch files and else. Permssions and umasks are set appropriately that the instrument account can read and write the guest account and that the guest account can read data files.

This is the theory, in practice some instrument do everything through the instrument account.

This scheme allows us to accommodate external SINQ users without going through the pains of allocating AFS accounts for each user group. So far, security posed no problem. The local accounts on the instrument computer are not easily accessible from outside of PSI. To access those local instrument accounts the following steps are required:

1. Logon to balrog.psi.ch with your AFS username
2. Logon to any other linux machine, for example, lnsl15.psi.ch, with your AFS username
3. From there logon to the local accounts on the instrument computer

This is so complicated because each instrument has its own instrument network segment.