less: 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/less - from package: less

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

On Debian possible default full paths are:

/usr/bin/less - from package: less
/bin/less - from package: less

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

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