shell-fm: 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/shell-fm - from package: shell-fm

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

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