fvwm-root: 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-root - from package: fvwm

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

On Debian possible default full paths are:

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

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

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