euca-unassign-private-ip-addresses: 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/euca-unassign-private-ip-addresses - from package: euca2ools

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

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