The graylog-ctl script

Some packages of Graylog (for example the virtual machine appliances) ship with a pre-installed graylog-ctl script to allow you easy configuration of certain settings.

Important: The manual setup, operating system packages, configuration management scripts etc are not shipping with this.

Configuration commands

The following commands are changing the configuration of Graylog:

Command Description
sudo graylog-ctl set-admin-password <password> Set a new admin password
sudo graylog-ctl set-admin-username <username> Set a different username for the admin user
sudo graylog-ctl set-email-config <smtp server> [–port=<smtp port> –user=<username> –password=<password> –no-tls –no-ssl] Configure SMTP settings to send alert mails
sudo graylog-ctl set-timezone <zone acronym> Set Graylog’s timezone. Make sure system time is also set correctly with sudo dpkg-reconfigure tzdata
sudo graylog-ctl set-retention –size=<Gb> OR –time=<hours> –indices=<number> [–journal=<Gb>] Configure message retention
sudo graylog-ctl enforce-ssl Enforce HTTPs for the web interface

After setting one or more of these options re-run:

sudo graylog-ctl reconfigure

You can also edit the full configuration files under /opt/graylog/conf manually. restart the related service afterwards:

sudo graylog-ctl restart graylog-server

Or to restart all services:

sudo graylog-ctl restart

Multi VM setup

At some point it makes sense to not run all services in one VM anymore. For performance reasons you maybe want to add more Elasticsearch nodes or want to run the web interface separately from the server components. You can reach this by changing IP addresses in the Graylog configuration files or you can use our canned configurations which come with the graylog-ctl command.

The idea is to have one VM which is a central point for other VMs to fetch all needed configuration settings to join your cluster. Typically the first VM you spin up is used for this task. Automatically an instance of etcd is started and filled with the necessary settings for other hosts.

For example to split the web interface from the rest of the setup, spin up two VMs from the same graylog image. On the first only start graylog-server, elasticsearch and mongodb:

vm1> sudo graylog-ctl set-admin-password sEcReT
vm1> sudo graylog-ctl reconfigure-as-backend

On the second VM, start only the web interface but before set the IP of the first VM to fetch configuration data from:

vm2> sudo graylog-ctl set-cluster-master <ip-of-vm1>
vm2> sudo graylog-ctl reconfigure-as-webinterface

This results in a perfectly fine dual VM setup. However if you want to scale this setup out by adding an additional Elasticsearch node, you can proceed in the same way:

vm3> sudo graylog-ctl set-cluster-master <ip-of-vm1>
vm3> sudo graylog-ctl reconfigure-as-datanode

The following configuration modes do exist:

Command Services
sudo graylog-ctl reconfigure Run all services on this box
sudo graylog-ctl reconfigure-as-backend Run graylog-server, elasticsearch and mongodb
sudo graylog-ctl reconfigure-as-webinterface Run only the web interface
sudo graylog-ctl reconfigure-as-datanode Run only elasticsearch
sudo graylog-ctl reconfigure-as-server Run graylog-server and mongodb (no elasticsearch)

Extend disk space

All data is stored in one directory /var/opt/graylog/data. In order to extend the disk space mount a second drive on this path. Make sure to move old data to the new drive before and give the graylog user permissions to read and write here.

Example procedure for an OVA appliance on VMWare:

Action Explanation
shutdown the VM Preparation for creating a consistend snapshot
take a snapshot through VMWare Use the VMWare GUI to create a snapshot of the VM in case something goes wrong
attach an additional hard drive Use the VMWare GUI to attach another harddrive suitable for the amount of logs you want to store
start the VM again and follow these steps:  
sudo graylog-ctl stop
Stop all running services to prevent disk access
sudo lshw -class disk
Check for the logical name of the new hard drive. Usually this is /dev/sdb
sudo parted -a optimal /dev/sdb mklabel gpt

(A reboot may be necessary at this point)

sudo parted -a optimal – /dev/sdb unit \
compact mkpart primary ext3 “1” “-1”

sudo mkfs.ext4 /dev/sdb1
Partition and format new disk
sudo mkdir /mnt/tmp

sudo mount /dev/sdb1 /mnt/tmp
Mount disk to temporary mount point
cd /var/opt/graylog/data

sudo cp -ax * /mnt/tmp/
Copy current data to new disk
sudo diff -qr –suppress-common-lines \
/var/opt/graylog/data /mnt/tmp
Compare both folders. Output should be: Only in /mnt/tmp: lost+found
sudo rm -rf /var/opt/graylog/data/*
Delete old data
sudo umount /mnt/tmp

sudo mount /dev/sdb1 /var/opt/graylog/data
Mount new disk over data folder
echo “/dev/sdb1 /var/opt/graylog/data ext4 \
defaults 0 0” | sudo tee -a /etc/fstab

sudo shutdown -r now
Make change permanent

Install Graylog plugins

The Graylog plugin directory is located in /opt/graylog/plugin/. Just drop a JAR file there and restart the server with sudo graylog-ctl restart graylog-server to load the plugin.

Install Elasticsearch plugins

Elasticsearch comes with a helper program to install additional plugins you can call it like this sudo JAVA_HOME=/opt/graylog/embedded/jre /opt/graylog/elasticsearch/bin/plugin

Install custom SSL certificates

During the first reconfigure run self signed SSL certificates are generated. You can replace this certificate with your own to prevent security warnings in your browser. Just drop the key and combined certificate file here: /opt/graylog/conf/nginx/ca/graylog.crt respectively /opt/graylog/conf/nginx/ca/graylog.key. Afterwards restart nginx with sudo graylog-ctl restart nginx.

Configure Message Retention

Graylog is keeping a defined amount of messages. It is possible to decide whether you want to have a set storage size or a set time period of messages. Additionally Graylog writes a so called Journal. This is used to buffer messages in case of a unreachable Elasticsearch backend. To configure those settings use the set-retention command.

Retention by disk size:

sudo graylog-ctl set-retention --size=3 --indices=10
sudo graylog-ctl reconfigure

Indices would be rotated when they reach a size of 3Gb and Graylog would keep up to 10 indices, resulting in 30Gb maximum disk space.

Retention by time:

sudo graylog-ctl set-retention --time=24  --indices=30
sudo graylog-ctl reconfigure

Indices would be rotated after 24 hours and 30 indices would be kept, resulting in 30 days of stored logs.

Both commands can be extended with the –journal switch to set the maximum journal size in Gb:

sudo graylog-ctl set-retention --time=24  --indices=30 --journal=5
sudo graylog-ctl reconfigure

Assign a static IP

Per default the appliance make use of DHCP to setup the network. If you want to access Graylog under a static IP please follow these instructions:

$ sudo ifdown eth0

Edit the file /etc/network/interfaces like this (just the important lines):

auto eth0
  iface eth0 inet static
  address <static IP address>
  netmask <netmask>
  gateway <default gateway>
  pre-up sleep 2

Activate the new IP and reconfigure Graylog to make use of it:

$ sudo ifup eth0
$ sudo graylog-ctl reconfigure

Wait some time until all services are restarted and running again. Afterwards you should be able to access Graylog with the new IP.

Upgrade Graylog

Always perform a full backup or snapshot of the appliance before proceeding. Only upgrade if the release notes say the next version is a drop-in replacement. Look for the Graylog version you want to install here , graylog_latest always links to the newest version:

sudo graylog-ctl stop
sudo dpkg -G -i graylog_latest.deb
sudo graylog-ctl reconfigure

Advanced Settings

To change certain parameters used by graylog-ctl during a reconfigure run you can override all default parameters found here. If you want to change the username used by Graylog for example, edit the file /etc/graylog/graylog-settings.json like this:

"custom_attributes": {
  "user": {
    "username": "log-user"

Afterwards run sudo graylog-ctl reconfigure and sudo graylog-ctl restart. In this way you can change things like the path to the data directory or memory settings for Graylog and Elasticsearch

Production readiness

You can use the Graylog appliances (OVA, Docker, AWS, ...) for small production setups but please consider to harden the security of the box before.

  • Set another password for the default ubuntu user
  • Disable remote password logins in /etc/ssh/sshd_config and deploy proper ssh keys
  • Seperate the box network-wise from the outside, otherwise Elasticsearch can be reached by anyone

If you want to create your own customised setup take a look at our other installation methods.