camlp4rf: 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/camlp4rf - from package: ocaml-camlp4-devel

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

On Debian possible default full paths are:

/usr/bin/camlp4rf - from package: camlp4-extra

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

Error in other languages:
camlp4rf: bevel nie gevind nie
camlp4rf: comandă negăsită
camlp4rf: comando não encontrado
camlp4rf: commande introuvable
camlp4rf: command not found
camlp4rf: käsku ei ole
camlp4rf: không tìm thấy lệnh
camlp4rf: komanda nerasta
camlp4rf: Kommando nicht gefunden.
camlp4rf: kommandot finns inte
camlp4rf: komut yok
camlp4rf: nie znaleziono polecenia
camlp4rf: níor aimsíodh an t-ordú
camlp4rf: no se encontró la orden
camlp4rf: no s'ha trobat l'ordre
camlp4rf: opdracht niet gevonden
camlp4rf: parancs nem található
camlp4rf: perintah tidak ditemukan
camlp4rf: príkaz nenájdený
camlp4rf: příkaz nenalezen
camlp4rf: команда не найдена
camlp4rf: командата не е открита
camlp4rf: 命令找不到
camlp4rf: コマンドが見つかりません