snfetch: 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/sbin/snfetch - from package: sn

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

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