readlink: 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/readlink - from package: coreutils
/usr/bin/readlink - from package: coreutils

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

On Debian possible default full paths are:

/bin/readlink - from package: coreutils
/usr/lib/klibc/bin/readlink - from package: klibc-utils

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

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