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

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Archive for the ‘*nix-tools’ Category

OpenSuSE: location of cron jobs

Posted by jpluimers on 2020/01/20

When you look at how to find listed cron jobs, usually the answer is cron -l or cron -u username -l.

However, on OpenSuSE systems, cron jobs can be in different places, and the sysconfig settings have influence on them too.

These files and directories all influence cron:

Directories:

/etc/cron.d/
/etc/cron.daily/
/etc/cron.hourly/
/etc/cron.monthly/
/etc/cron.weekly/

Files:

/etc/sysconfig/cron
/etc/init.d/rc2.d/K01cron
/etc/init.d/rc2.d/S14cron
/etc/init.d/rc3.d/K01cron
/etc/init.d/rc3.d/S14cron
/etc/init.d/rc5.d/K01cron
/etc/init.d/rc5.d/S14cron
/etc/init.d/cron
/etc/news/crontab.sample
/etc/pam.d/crond
/etc/systemd/system/multi-user.target.wants/cron.service
/etc/omc/srvinfo.d/cron.xml
/etc/cron.deny
/etc/crontab

Most are available for other Linux distributions as well, but each one might have slightly different configurations (especially for the directories). Some background reading:

Some details:

  • The crontab -l will only list what is in /etc/crontab.
  • These directories are influenced by/etc/sysconfig/cron, especially the DAILY_TIME variable (see below) for the daily jobs.
    All of the directories are checked every 15 minutes through /usr/lib/cron/run-crons:/etc/cron.daily/
    /etc/cron.hourly/
    /etc/cron.monthly/
    /etc/cron.weekly/
  • That script then uses these files for checking when to run:/var/spool/cron/lastrun/cron.weekly
    /var/spool/cron/lastrun/cron.daily
    /var/spool/cron/lastrun/cron.hourly

The DAILY_TIME variable:

## Type: string
## Default: ""
#
# At which time cron.daily should start. Default is 15 minutes after booting
# the system. Example setting would be "14:00".
# Due to the fact that cron script runs only every 15 minutes,
# it will only run on xx:00, xx:15, xx:30, xx:45, not at the accurate time
# you set.
DAILY_TIME=""

–jeroen

 

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

a perf cheat sheet from @brendangregg’s fantastic web page;  you can print it as PDF

Posted by jpluimers on 2020/01/13

From a while back: [WayBack⚡Julia Evans⚡ on Twitter : made a perf cheat sheet from @brendangregg’s fantastic https://t.co/SBDtzn0G8J. you can print it at https://t.co/xC6ndjrSDL https://t.co/TstbBBe3DS

References:

The latter has a lot of examples and even more explanation all around the below picture.

–jeroen

Read the rest of this entry »

Posted in *nix, *nix-tools, Development, Linux, Power User, Profiling-Performance-Measurement | Leave a Comment »

imagemagick – Command line convert webp to jpg? – Unix & Linux Stack Exchange

Posted by jpluimers on 2019/12/23

For my link archive: [WayBack] imagemagick – Command line convert webp to jpg? – Unix & Linux Stack Exchange

–jeroen

Posted in *nix, *nix-tools, Google, GoogleWebP, Image Editing, Power User, The Gimp | Leave a Comment »

Magic SysRq key – Wikipedia

Posted by jpluimers on 2019/12/20

Cool: Magic SysRq key – Wikipedia

The magic SysRq key is a key combination understood by the Linux kernel, which allows the user to perform various low-level commands regardless of the system’s state. It is often used to recover from freezes, or to reboot a computer without corrupting the filesystem.[1] Its effect is similar to the computer’s hardware reset button (or power switch) but with many more options and much more control.

Sometimes reading fluffy fluff posts teaches you new things, so be sure to read this one:

[WayBack] I just got trolled by my cat, hard. Last night i left my linux laptop open and running while watching TV in the other room. I came back to find Marley … – Stephen Shirley – Google+

I started looking through the kernel logs from last night, to see if there was any indication of the issue starting. And then i saw it. One innocent line that said:

Dec 18 21:26:52 x240 kernel: [373001.156356] sysrq: SysRq : Emergency Remount R/O

The fluffy dumbass had somehow hit the Sysrq [0] key combo to mount all filesystems read-only. This is an old, low-level when-all-else-fails facility for dealing with an linux unresponsive system, and fluff-for-brains Marley had somehow hit alt+fn+s+u.

Sigh.

[0] https://en.wikipedia.org/wiki/Magic_SysRq_key

Via: [Archive.is] I just got trolled by my cat, hard. Last night i left my linux laptop open and running while watching TV in the other room. I came back to find Marley … – Kristian Köhntopp – Google+

–jeroen

Posted in *nix, *nix-tools, Keyboards and Keyboard Shortcuts, Linux, Power User | Leave a Comment »

bash: converting numbers to human readable SI or IEC units

Posted by jpluimers on 2019/12/03

Many unix tools that report sizes in bytes can convert them to either IEC or SI readable formats.

For github.com/jpluimers/btrfs-du/blob/master/btrfs-du I wrote about last week, I also wanted that kind of behaviour. So I did some research and came up with the code and test cases below.

Note that depending on the bitness of your system, bash integer numeric values are limited in size; see [WayBack] What is the maximum value of a numeric bash shell variable? – Super User.

So I wrote a small bash script for that too, which needed also gave me the opportunity to show how a  perpetual while loop as explained by [WayBack] bash – “while :” vs. “while true” – Stack Overflow.

Two things that always bite me with these short scripts are expressions (done through [WayBack]Arithmetic Expansion) and comparisons (through[WayBack] Other Comparison Operators).

The IEC suffixes contain one extra i to indicate binary and – next to the ISO notation that were already ISO defined – made it into the ISO 80000 standard since 2008. Here is a comparison list from [WayBackBinary prefix – Wikipedia:

Prefixes for multiples of
bits (bit) or bytes (B)
Decimal
Value SI
1000 k kilo
10002 M mega
10003 G giga
10004 T tera
10005 P peta
10006 E exa
10007 Z zetta
10008 Y yotta
Binary
Value IEC JEDEC
1024 Ki kibi K kilo
10242 Mi mebi M mega
10243 Gi gibi G giga
10244 Ti tebi
10245 Pi pebi
10246 Ei exbi
10247 Zi zebi
10248 Yi yobi

Most tools nowadays default to binary IEC suffixes for byte sizes, though disk manufacturers still use SI suffixes because, well then they appear bigger but aren’t. Just for comparison, look at the numbers from [WayBack] File size – Wikipedia and [WayBack] IEC and SI Size Notations – AN!Wiki where I got the test cases from:

Read the rest of this entry »

Posted in *nix, *nix-tools, bash, bash, Development, Power User, Scripting, Software Development | Leave a Comment »

 
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