unison-latest-stable-gtk: 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-gtk - from package: unison-gtk

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

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