rmkdepend: 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/rmkdepend - from package: root-core

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

On Debian possible default full paths are:

/usr/bin/rmkdepend - from package: libroot-core-dev

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

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