xkeycaps: 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/xkeycaps - from package: xkeycaps

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

On Debian possible default full paths are:

/usr/bin/xkeycaps - from package: xkeycaps

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

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