g3cat: 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/g3cat - from package: mgetty

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

On Debian possible default full paths are:

/usr/bin/g3cat - from package: mgetty-fax

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

Error in other languages:
g3cat: bevel nie gevind nie
g3cat: comandă negăsită
g3cat: comando não encontrado
g3cat: commande introuvable
g3cat: command not found
g3cat: käsku ei ole
g3cat: không tìm thấy lệnh
g3cat: komanda nerasta
g3cat: Kommando nicht gefunden.
g3cat: kommandot finns inte
g3cat: komut yok
g3cat: nie znaleziono polecenia
g3cat: níor aimsíodh an t-ordú
g3cat: no se encontró la orden
g3cat: no s'ha trobat l'ordre
g3cat: opdracht niet gevonden
g3cat: parancs nem található
g3cat: perintah tidak ditemukan
g3cat: príkaz nenájdený
g3cat: příkaz nenalezen
g3cat: команда не найдена
g3cat: командата не е открита
g3cat: 命令找不到
g3cat: コマンドが見つかりません