lpadmin: 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/sbin/lpadmin - from package: cups

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

On Debian possible default full paths are:

/usr/sbin/lpadmin - from package: cups-client

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

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