====== Linux/Prepare ======

===== Basic =====

==== default EDITOR ====
<code bash>
sudo update-alternatives --list editor
sudo update-alternatives --config editor
</code>

==== set umask ====

In file: ''~/.profile''
  * ''umask 002'' (default), RW for user, RW for group and R for others - create dirs as 775 and files as 664
  * ''umask 022'' (default for root), 755 and 644
  * ''umask 077'' only RW for user, not other access
  * ''umask 007'' RW for user, RW for group

**NOTE!:** Problem appears with non default user umask and ''sudo'' command usage.
After sudo umask is still set to the user umask, which is correct. 
But can lead to some unpredicted behavior i.e. installing system-wide packages - new file will be created with incorrect umasks (user umask).

To prevent this:
<file | /etc/sudoers>
Defaults        umask_override
Defaults        umask=0022
</file>


==== add i386 architecture ====

<code bash>
dpkg --add-architecture i386
apt-get update
apt-get install gpm tcpdump bmon tinc ppp pptpd mc links2 gparted hdparm smartmontools smart-notifier valgrind openssh-server
apt-get install wireshark mtr
</code>

==== NTP: allow time corrections bigger than 1h ====
  - Disable systemd time service: ''systemctl disable --now systemd-timesyncd''
  - Install ''ntpdate'' and ''ntp''
  - Edit ''/etc/default/ntp'' and add ''-g'' argument. 
  - Switch RTC to UTC time:
<code bash>
timedatectl set-local-rtc 0
ntpd -gxn
hwclock --systohc
</code>




==== Disable PC speaker ====
<code bash>
echo "blacklist pcspkr" > /etc/modprobe.d/nobeep.conf
</code>

==== resolv.conf ====
<code bash>apt-get install resolvconf</code>

Add own nameserver into **/etc/resolvconf/resolv.conf.d/base**

<code ini>nameserver 8.8.8.8</code>
and execute
<code bash>sudo resolvconf -u</code>

=== Polish & locales ===
<code bash>
dpkg-reconfigure keyboard-configuration
apt-get install console-data
dpkg-reconfigure console-data
dpkg-reconfigure locales
</code>

add 
  * pl_PL
  * pl_PL.UTF-8

In Debian, locales are handled in /etc/default/locale. File /etc/environment is deprecated.
<code bash>
grep pam_env.so /etc/pam.d/*
...
/etc/pam.d/login:session       required   pam_env.so readenv=1
/etc/pam.d/login:session       required   pam_env.so readenv=1 envfile=/etc/default/locale
...
</code>


Remember to set [[sw:libreoffice#paper_format]]

==== set cfq/deadline scheduler ====

<file | /etc/udev/rules.d/60-schedulers.rules>
#ACTION=="add|change", KERNEL=="sd*[!0-9]|sr*", ATTR{queue/rotational}=="1", ATTR{queue/scheduler}="cfq"
ACTION=="add|change", KERNEL=="sd*[!0-9]|sr*", ATTR{queue/rotational}=="1", ATTR{queue/scheduler}="bfq"
# ACTION=="add|change", KERNEL=="sd*[!0-9]|sr*|mmcblk[0-9]*", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="deadline"  
ACTION=="add|change", KERNEL=="sd*[!0-9]|sr*|mmcblk[0-9]*", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="kyber"
ACTION=="add|change", KERNEL=="nvme[0-9]n[0-9]*", ATTR{queue/scheduler}="kyber"
</file>

<code bash>cat /sys/block/sd*/queue/scheduler</code>

=== single queue schedulers ===
There are 2 queues, one for read & one for write operations.
  * **none** is just a First In First Out standard queue of I/O operations.
  * **cfq** (Completely Fair Scheduling) is similar to the Round Robin algorithm and basically allots a fixed execution time for each I/O operation (they are implemented as a circular queue)
  * **deadline** is like a priority queue with an aging concept. Basically it adds a deadline for each I/O operation & implements a priority queue

=== block multi-queue schedulers ===
Supported in kernel >=4.12. It is disabled by default.
To use multi-queue schedulers compile kernel with **CONFIG_SCSI_MQ_DEFAULT=y** or pass parameter **scsi_mod.use_blk_mq=1** in boot loader.

[[https://www.thomas-krenn.com/en/wiki/Linux_Multi-Queue_Block_IO_Queueing_Mechanism_(blk-mq)|Linux Multi-Queue Block IO Queueing Mechanism]]

<file | /etc/udev/rules.d/60-schedulers.rules>
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="1", ATTR{queue/scheduler}="bfq"
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="mq-deadline"
</file>
<code bash>
sudo udevadm control --reload
sudo udevadm trigger
cat /sys/block/sd*/queue/scheduler
</code>

==== Disable console beep ====

To disable console annoying beep:
 * System wide by removing PC Speaker module:
<code bash>
rmmod pcspkr
sudo echo "blacklist pcspkr" > /etc/modprobe.d/pcspkr-blacklist.conf
</code>





===== Usefull software =====
<code bash>sudo apt-get install wireshark cups</code>
<code bash>sudo usermod -G lp,lpadmin,dialout,sudo,audio,video,netdev,vboxusers,wireshark,kismet,i2c user_login</code>


==== parallel packers ====
<code bash>sudo apt-get install pigz pbzip2 pxz lbzip2</code>

To force using parallel packers system-wide:
<code bash>
ln -s /usr/bin/lbzip2 /usr/local/bin/bzip2
ln -s /usr/bin/lbzip2 /usr/local/bin/bunzip2
ln -s /usr/bin/lbzip2 /usr/local/bin/bzcat
ln -s /usr/bin/pigz /usr/local/bin/gzip
ln -s /usr/bin/pigz /usr/local/bin/gunzip
ln -s /usr/bin/pigz /usr/local/bin/zcat
ln -s /usr/bin/pixz /usr/local/bin/xz
</code>
or use bash aliases:
<file | .bashrc>
alias gzip='pigz'
alias gunziip='unpigz'
alias bzip2='pbzip2'
alias bunzip2='pbunzip2'
alias xz='pxz'
</file>

some benchmarks (i7-3770K), BTRFS FS +NoCOW attrib
^ command    ^ user time ^ size ^ comments ^
|pbzip2 -1   | 4m12       | 694M |         | 
|pbzip2 -5   | 4m59       | 683M |         |
|pbzip2 -9   | 6m25       | 679M | default |
|pigz -0     | 0m32       | 3,5G | no compression |
|pigz -1     | 0m52       | 727M |         |
|pigz -2     | 0m48       | 723M |         |
|pigz -6     | 1m18       | 698M | default |
|pxz -0      | 3m30       | 660M |         | 
|pxz -3      | 5m00       | 636M |         |
|pxz -6      | 11m19      | 571M | default |




==== etckeeper ====
<code bash>
apt-get install git 
git config --global user.name "my name"
git config --global user.email myemail@address.pl
apt-get install git-cola etckeeper kdiff3
</code>


==== mandb ====

Disable mandb updates after apt:
<code bash>echo "set man-db/auto-update false" | debconf-communicate; dpkg-reconfigure man-db</code>