ed: 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/ed - from package: ed

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

On Debian possible default full paths are:

/bin/ed - from package: ed
/usr/lib/plan9/bin/ed - from package: 9base

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

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