isync: 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/isync - from package: isync

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

On Debian possible default full paths are:

/usr/bin/isync - from package: isync

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

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