idevicebackup: 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/idevicebackup - from package: libimobiledevice

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

On Debian possible default full paths are:

/usr/bin/idevicebackup - from package: libimobiledevice-utils

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

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