faxaddmodem: 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/sbin/faxaddmodem - from package: hylafax+

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

On Debian possible default full paths are:

/usr/sbin/faxaddmodem - from package: hylafax-server

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

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