bash: 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:

/bin/bash - from package: bash

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

On Debian possible default full paths are:

/bin/bash - from package: bash

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

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