osm2pgsql: 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/bin/osm2pgsql - from package: osm2pgsql

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

Error in other languages:
osm2pgsql: bevel nie gevind nie
osm2pgsql: comandă negăsită
osm2pgsql: comando não encontrado
osm2pgsql: commande introuvable
osm2pgsql: command not found
osm2pgsql: käsku ei ole
osm2pgsql: không tìm thấy lệnh
osm2pgsql: komanda nerasta
osm2pgsql: Kommando nicht gefunden.
osm2pgsql: kommandot finns inte
osm2pgsql: komut yok
osm2pgsql: nie znaleziono polecenia
osm2pgsql: níor aimsíodh an t-ordú
osm2pgsql: no se encontró la orden
osm2pgsql: no s'ha trobat l'ordre
osm2pgsql: opdracht niet gevonden
osm2pgsql: parancs nem található
osm2pgsql: perintah tidak ditemukan
osm2pgsql: príkaz nenájdený
osm2pgsql: příkaz nenalezen
osm2pgsql: команда не найдена
osm2pgsql: командата не е открита
osm2pgsql: 命令找不到
osm2pgsql: コマンドが見つかりません