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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for the ‘*nix’ Category

Introduction to Snapshots/Rollback with Snapper | ActiveDoc

Posted by jpluimers on 2019/07/01

The snapper documentation itself is big and hard to grasp at once, so start here for a few examples on how to get going, or how to assess your current configuration:

For a very good snapper introduction seems to be gone, but was present in the OpenSuSE documentation archive circa version 13.2 at [WayBackChapter 4. Snapshots/Rollback with Snapper | ActiveDoc which I’ve quoted below.

Between that version and LEAP, the retention got moved from “timeline” based to “number” based. More on that in these links:

Man pages:

Introduction

4.1.1 snapshots and Disk Space #

When a snapshot is created, both the snapshot and the original point to the same blocks in the file system. So, initially a snapshot does not occupy additional disk space. If data in the original file system is modified, changed data blocks are copied while the old data blocks are kept for the snapshot. Therefore, a snapshot occupies the same amount of space as the data modified. So, over time, the amount of space a snapshot allocates, constantly grows. As a consequence, deleting files from a Btrfs file system containing snapshots may not free disk space!

Note: Snapshot Location

Snapshots always reside on the same partition or subvolume that has been snapshotted. It is not possible to store snapshots on a different partition or subvolume.

As a result, partitions containing snapshots need to be larger than “normal” partitions. The exact amount strongly depends on the number of snapshots you keep and the amount of data modifications. As a rule of thumb you should consider using twice the size than you normally would.

Tip: Freeing space / Disk Usage

In order to free space on a Btrfs partition containing snapshots you need to delete unneeded snapshots rather than files. Older snapshots occupy more space than recent ones.

Since the df does not show the correct disk usage on Btrfs file systems, you need to use the command btrfs filesystem df MOUNT_POINT. Displaying the amount of disk space a snapshot allocates is currently not supported by the Btrfs tools.

–jeroen

Posted in *nix, Linux, openSuSE, Power User, SuSE Linux, Tumbleweed | Leave a Comment »

Some links about the TCP SACK PANIC attacks on Linux and FreeBSD Kernels

Posted by jpluimers on 2019/06/20

The TCP SACK vulnerabilities as found by Netflix: [WayBack] security-bulletins/2019-001.md at master · Netflix/security-bulletins · GitHub.

Easy, but slow workaround from [WayBack] linux – How to disable TCP SACK for CentOS? – Super User:

Temporary (until boot):

echo "0" > /proc/sys/net/ipv4/tcp_sack

Permanent (even after boot):

echo "net.ipv4.tcp_sack = 0" >> /etc/sysctl.conf
sysctl -p

Coverage:

–jeroen

Posted in *nix, *nix-tools, Communications Development, Development, Internet protocol suite, Power User, Security, TCP | Leave a Comment »

CitiZen nmap output

Posted by jpluimers on 2019/06/14

CitiZen nmap output: beagleboard with these open ports:

  • 22 – ssh
  • 80 – http
  • 81 – unknown
  • 1883 – mqtt
  • 35505 – http

–jeroen

Posted in *nix, *nix-tools, nmap, Power User | Leave a Comment »

ls colour codes on OpenSuSE tumbleweed when accessed from Mac OS X ssh

Posted by jpluimers on 2019/06/07

`ls` colour codes

`ls` colour codes

I got confused as I thought red text would mean an error.

But they’re not: greenish yellow on a read background means error (a symbolic link to a place that’s no longer there).

It’s the output of https://github.com/gkotian/gautam_linux/blob/master/scripts/colours.sh as the one at

Actually the script is here https://raw.githubusercontent.com/gkotian/gautam_linux/master/scripts/colours.sh as the one at [WayBackcommand line – What do the different colors mean in the terminal? – Ask Ubuntu failed with errors like this one:

-bash: *.xbm: bad substitution

The full script output is below.

Since various terminals have a different mapping from colours in the ANSI escape code colour table, I used the standard HTML colours using (which slightly differs from the Terminal.app screenshot on the right):

References:

Note that the shell on Mac OS X uses a different way of configuring colours CLICOLOR as described in [WayBacksettings – CLICOLOR and LS_COLORS in bash – Unix & Linux Stack Exchange. I might cover that another day.

Script output:

Read the rest of this entry »

Posted in *nix, *nix-tools, bash, CSS, Development, HTML, HTML5, Linux, openSuSE, Power User, Software Development, SuSE Linux, Tumbleweed, Web Development | Leave a Comment »

svnrdump for dumping and loading remote svn repositories – twm’s blog

Posted by jpluimers on 2019/05/31

One day I will likely need svnrdump:

Since I keep forgetting what the tool is called and how to use it: svnrdump is a tool that can dump a remote svn repostory to a text file and also load that text file into a different remote svn repository…

Via: [WayBack] Since I keep forgetting what the tool is called and how to use it: svnrdump i…

–jeroen

Posted in *nix, Development, DVCS - Distributed Version Control, Power User, Subversion/SVN, Windows | Leave a Comment »

 
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