fastafetch: 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/fastafetch - from package: exonerate

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

On Debian possible default full paths are:

/usr/bin/fastafetch - from package: exonerate

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

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