gsissh-keygen: 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-keygen - from package: gsi-openssh

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

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