akonadi_control: 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/akonadi_control - from package: akonadi

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

On Debian possible default full paths are:

/usr/bin/akonadi_control - from package: akonadi-server

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

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