idxmerge: 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/idxmerge - from package: fweb

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

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