rds-ctl: 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/rds-ctl - from package: v4l-utils

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

On Debian possible default full paths are:

/usr/bin/rds-ctl - from package: v4l-utils

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

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