fvwm-config: 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/fvwm-config - from package: fvwm

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

On Debian possible default full paths are:

/usr/bin/fvwm-config - from package: fvwm

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

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