screenfetch: 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/screenfetch - from package: screenfetch

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

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