The Globus package containing gsissh (and its scp/ftp-ing brethren) isn’t in the standard Ubuntu repositories. In the past I’ve had to install bloated packages to use it (e.g. within the LIGO Scientific Collaboration we have the LDG Client, which contains many things that the average user doesn’t need). Relatively recently I found the stand-alone package from globus that I need to just get gsissh: gsi-openssh-clients (the link takes you to the latest stable v5.2 version for Ubuntu 12.04, but if you edit the link appropriately [go down to the /gt5 part] you can find the older version, or verions for older Ubuntu/Debian distros, and also rpms for Centos/Fedoro/etc). From the link download the appropriate .deb version of gsi-openssh-clients***.deb and install it with dpkg. Alternatively, and maybe more sensibly, add e.g.
deb http://www.globus.org/ftppub/gt5/5.2/stable/packages/deb/ubuntu/12.04 precise contrib
to your /etc/apt/source.list file and install via
sudo apt-get update; sudo apt-get install gsi-openssh-clients
This is mainly here to remind me of the location as I’ve been asked about it a couple of times and often forget.
Note: to use gsissh you will need to install some globus packages that are within the standard Ubuntu repositories e.g. sudo apt-get install globus-proxy-utils (which will install most, if not all, of the required dependencies)
Also note: a lot of the time when gsissh-ing you need to have the bundle of X509 trusted certificates (often installed in /etc/grid-security/certificates). If you don’t have this then you can download the latest osg-ca-certs .deb package from here and install it using e.g.:
sudo dpkg -i osg-ca-certs_1.31NEW-0_all.deb
.