gsissh: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/gsissh - from package: gsi-openssh-clients

You may install the required package with command yum install {package}

Error in other languages:
gsissh: bevel nie gevind nie
gsissh: comandă negăsită
gsissh: comando não encontrado
gsissh: commande introuvable
gsissh: command not found
gsissh: käsku ei ole
gsissh: không tìm thấy lệnh
gsissh: komanda nerasta
gsissh: Kommando nicht gefunden.
gsissh: kommandot finns inte
gsissh: komut yok
gsissh: nie znaleziono polecenia
gsissh: níor aimsíodh an t-ordú
gsissh: no se encontró la orden
gsissh: no s'ha trobat l'ordre
gsissh: opdracht niet gevonden
gsissh: parancs nem található
gsissh: perintah tidak ditemukan
gsissh: príkaz nenájdený
gsissh: příkaz nenalezen
gsissh: команда не найдена
gsissh: командата не е открита
gsissh: 命令找不到
gsissh: コマンドが見つかりません