ovsdb-server: 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 Debian possible default full paths are:

/usr/lib/debug/usr/sbin/ovsdb-server - from package: openvswitch-dbg
/usr/sbin/ovsdb-server - from package: openvswitch-switch

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

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