ssindex: 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/ssindex - from package: gnumeric

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

On Debian possible default full paths are:

/usr/bin/ssindex - from package: gnumeric

You may install the required package with command apt-get install {package}

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