sync_server: command not found

Have You tried accessing the binary with the full path?

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/lib/cyrus/bin/sync_server - from package: cyrus-replication

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