unison-latest-stable: 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 Debian possible default full paths are:

/usr/bin/unison-latest-stable - from package: unison

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

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