c2faxsend: 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/c2faxsend - from package: capi4hylafax

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

Error in other languages:
c2faxsend: bevel nie gevind nie
c2faxsend: comandă negăsită
c2faxsend: comando não encontrado
c2faxsend: commande introuvable
c2faxsend: command not found
c2faxsend: käsku ei ole
c2faxsend: không tìm thấy lệnh
c2faxsend: komanda nerasta
c2faxsend: Kommando nicht gefunden.
c2faxsend: kommandot finns inte
c2faxsend: komut yok
c2faxsend: nie znaleziono polecenia
c2faxsend: níor aimsíodh an t-ordú
c2faxsend: no se encontró la orden
c2faxsend: no s'ha trobat l'ordre
c2faxsend: opdracht niet gevonden
c2faxsend: parancs nem található
c2faxsend: perintah tidak ditemukan
c2faxsend: príkaz nenájdený
c2faxsend: příkaz nenalezen
c2faxsend: команда не найдена
c2faxsend: командата не е открита
c2faxsend: 命令找不到
c2faxsend: コマンドが見つかりません