dir: 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/dir - from package: coreutils

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

On Debian possible default full paths are:

/bin/dir - from package: coreutils

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

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