OpenSource software should be encouraged more…
Interesting article on Linux permissions. It explains how to recognise which permission system might be in use (SELinux, ACLs), the meaning of the special bits (setuid, setgid, sticky), how umask works, and more.
The basic Linux permission model — owner, group, others with read/write/execute — is ju[……]
Need to know the dynamic IP ranges used by AWS in a specific region? AWS publishes this as a JSON file.
curl -s https://ip-ranges.amazonaws.com/ip-ranges.json | jq '.prefixes | .[] | select((.region == "eu-west-1") and (.service == "EC2")) | .ip_prefix' | sed 's/"//g'
This filters for EC2 in eu-we[……]
Interesting article on the different levels and skill sets of System Administrators. It breaks down what separates a junior sysadmin from a senior one and the kind of knowledge you accumulate along the way.
Whether you are just starting out or have been managing servers for years, it is a good read[……]
Open Source software was becoming more and more popular in 2009, even though many of these applications were still little known. According to PCWorld, here are ten of the greatest.
Firefox — The open source browser that challenged Internet Explorer and changed the web.
Chromium — The open source pro[……]
Sometimes disks stop responding and cause system slowness because the kernel is waiting for a response that never comes. The disk appears 100% utilised in iostat even though nothing is being read or written.
To avoid rebooting, reset the device. First find it:
lsscsi
Then remove and rescan:
echo[......]
When dealing with hardware, you often see log messages like:
ata9: hard resetting link
ata9: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
To map an ata number to the actual sdX device:
ls -l /sys/class/ata_device/ata9/device/host*/target*/*/block
This shows which sdX corresponds to ata9. Che[……]
Somebody had the brilliant idea of using Unix timestamps in Squid log files. It makes parsing easy but reading them is not so human-friendly.
This is an elegant way of solving the problem:
cat /var/log/squid/access.log | perl -p -e 's/^([0-9]*)/"[" . localtime($1) . "]"/e'
The Perl one-liner captu[……]
Say you have a file called test.txt:
line 1
line 2
line 3
Remove the first line:
tail -n +2 test.txt
Remove the last line:
head -n -1 test.txt
Remove both:
tail -n +2 test.txt | head -n -1
Simple, portable, works on any Unix system.
Enjoy!
[……]
I had to make modifications to several BIND zone files. Sed proved itself invaluable once again.
The zone files looked like this:
domain.com. IN SOA ns1.domain.com. postmaster.domain.com. (
2015021001 ; Serial
600 ; Refresh (10 minutes)
1800[......]
Sometimes when creating one-liners, the source contains non-ASCII characters that make parsing harder. To strip them all out, use Perl:
cat dirty-source.txt | perl -pe 's/[^[:ascii:]]//g' > clean-output.txt
This replaces every character that is not in the ASCII set with nothing, leaving only clean[……]