wall: 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/wall - from package: sysvinit-tools

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

On Debian possible default full paths are:

/usr/bin/wall - from package: bsdutils

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

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