ospf_clear_database: command not found

Have You tried accessing the binary with the full path?

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/xorp/bin/ospf_clear_database - from package: xorp

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