4channels: 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/4channels - from package: LibRaw-samples

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

Error in other languages:
4channels: bevel nie gevind nie
4channels: comandă negăsită
4channels: comando não encontrado
4channels: commande introuvable
4channels: command not found
4channels: käsku ei ole
4channels: không tìm thấy lệnh
4channels: komanda nerasta
4channels: Kommando nicht gefunden.
4channels: kommandot finns inte
4channels: komut yok
4channels: nie znaleziono polecenia
4channels: níor aimsíodh an t-ordú
4channels: no se encontró la orden
4channels: no s'ha trobat l'ordre
4channels: opdracht niet gevonden
4channels: parancs nem található
4channels: perintah tidak ditemukan
4channels: príkaz nenájdený
4channels: příkaz nenalezen
4channels: команда не найдена
4channels: командата не е открита
4channels: 命令找不到
4channels: コマンドが見つかりません