walk: 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/lib64/4ti2/bin/walk - from package: 4ti2

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

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