mod_gearman_worker: 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

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/sbin/mod_gearman_worker - from package: mod-gearman-worker

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