update-patterndb: 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/update-patterndb - from package: syslog-ng

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

On Debian possible default full paths are:

/usr/bin/update-patterndb - from package: syslog-ng-core

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

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