Live Boot Differences

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General Live Boot Questions

There are significant differences between live booting a NST ISO versus booting a NST system after installing it to hard disk. This page discusses some of the differences.

Why does a live boot continually to consume RAM?

When you perform a live boot from a read only ISO file system, the operating system installs a special overlay for the file system that keeps track of write operations. When you attempt to write to a file within the ISO file system, the overlay traps the operation and copies the write to memory instead. Each time one of these write operations occurs, RAM is allocated by the overlay system to hold the new contents of the file. This eats away at available memory and will eventually cause the system to crash.

Because of this, you should never expect a live boot to run for a extended period of time. A live boot may only run for minutes, hours or days (depending on the amount of file activity) before it crashes whereas a full hard disk installation should run indefinitely.

Why isn't information saved between live boots?

Since live boots are designed to run from read only file systems (like DVD media), there is no ability to automatically persist information between boots.

However, if you use the livecd-iso-to-disk tool to create a pseudo live boot USB memory stick, there are options which available which allow you to allocate space on the USB disk to be used as an overlay for the root file system for persisting information between sessions. This pseudo live boot is more similar to a live boot system than a full hard disk installation as the persistence layer will eventually fill over time and need to be cleared. Using the livecd-iso-to-disk tool, it is also possible to allocate a separate /home partition which will behave like a normally mounted partition.

Why would I want to live boot?

There are several reasons why you would want to live boot from a NST ISO image:

  • To try out the NST distribution before committing to a hard disk installation.
  • To install the NST distribution to a disk.
  • To troubleshoot problems on a existing system.

What are some configuration differences between a live boot and a hard disk installation?

How is /etc/systemd/journald.conf modified on a live boot?

Starting with the NST 20 release, we decided to disable the logging of journalctl messages. This helps reduce the rate of RAM consumption during a live boot session.

To re-enable the logging of journal messages, change the Storage mode option from "none" back to "auto" in "/etc/systemd/journald.conf". For example:

[Journal]
Storage=auto
#Compress=yes
#Seal=yes
#SplitMode=login
#SyncIntervalSec=5m
#RateLimitInterval=30s
#RateLimitBurst=1000
#SystemMaxUse=
#SystemKeepFree=
#SystemMaxFileSize=
#RuntimeMaxUse=
#RuntimeKeepFree=
#RuntimeMaxFileSize=
#MaxRetentionSec=
#MaxFileSec=1month
#ForwardToSyslog=yes
#ForwardToKMsg=no
#ForwardToConsole=no
#TTYPath=/dev/console
#MaxLevelStore=debug
#MaxLevelSyslog=debug
#MaxLevelKMsg=notice
#MaxLevelConsole=info

After making the change, you will need to restart the systemd-journald.service:

[root@taco-dev64 ~]# systemctl restart systemd-journald.service
[root@taco-dev64 ~]#