apache2: 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 Debian possible default full paths are:

/usr/sbin/apache2 - from package: apache2-bin
/usr/lib/debug/usr/sbin/apache2 - from package: apache2-dbg

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

Error in other languages:
apache2: bevel nie gevind nie
apache2: comandă negăsită
apache2: comando não encontrado
apache2: commande introuvable
apache2: command not found
apache2: käsku ei ole
apache2: không tìm thấy lệnh
apache2: komanda nerasta
apache2: Kommando nicht gefunden.
apache2: kommandot finns inte
apache2: komut yok
apache2: nie znaleziono polecenia
apache2: níor aimsíodh an t-ordú
apache2: no se encontró la orden
apache2: no s'ha trobat l'ordre
apache2: opdracht niet gevonden
apache2: parancs nem található
apache2: perintah tidak ditemukan
apache2: príkaz nenájdený
apache2: příkaz nenalezen
apache2: команда не найдена
apache2: командата не е открита
apache2: 命令找不到
apache2: コマンドが見つかりません