count_unknown_ext: 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/count_unknown_ext - from package: sloccount

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

On Debian possible default full paths are:

/usr/bin/count_unknown_ext - from package: sloccount

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

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