xapian-config: 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/xapian-config - from package: xapian-core-devel
/usr/bin/xapian-config - from package: xapian-core

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

On Debian possible default full paths are:

/usr/bin/xapian-config - from package: libxapian-dev

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

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