1. benchmarkin the local disk

dd if=/dev/zero of=./xx conv=fdatasync bs=1M count=1000; rm -fv ./xx

2. grub2

2.1. splash boot screen

wget -nv http://d01cid.ddns.net/sharel/pic/centos7.jpg -O /boot/grub2/splash.jpg
sed -i 's/GRUB_TERMINAL_OUTPUT=/#GRUB_TERMINAL_OUTPUT=/' /etc/default/grub
echo 'GRUB_GFXMODE="800x600"' >> /etc/default/grub
echo 'GRUB_BACKGROUND="/boot/grub2/splash.jpg"' >> /etc/default/grub
grub2-mkconfig -o /boot/grub2/grub.cfg

3. reset root password

boot to rescue mode by adding rd.break as a kernel parameter

mount -o remount,rw /sysroot
chroot /sysroot
echo root:newpasswd | chpasswd
exit
reboot

4. samba

4.1. samba automount with autofs

as root

yum -y install autofs
systemctl enable autofs.service

as a user

mkdir -p ~/etc/autofs
vi ~/etc/autofs/master.autofs
/home/asterix/nas /home/jeehan/etc/autofs/user.autofs --timeout=600 --ghost
vi ~/etc/autofs/user.autofs
music -fstype=cifs,vers=1.0,rw,noperm,user=jeehan,pass=Passw0rd ://nas.d01.net/music
photo -fstype=cifs,vers=1.0,rw,noperm,user=jeehan,pass=Passw0rd ://nas.d01.net/photo
video -fstype=cifs,vers=1.0,rw,noperm,user=jeehan,pass=Passw0rd ://nas.d01.net/video
Tip you can store the credentials into a separate file
music -fstype=cifs,vers=1.0,rw,noperm,credentials=/home/jeehan/etc/autofs/upm.autofs ://nas.d01.net/music
vi ~/etc/autofs/upm.autofs
username=jeehan
password=Passw0rd

as root

ln -sv /home/jeehan/etc/autofs/master.autofs /etc/auto.master.d/
systemctl start autofs.service

5. systemctl

5.1. journal log files under /var/log/journal/

journalctl --disk-usage
journalctl --vacuum-size=64M
journalctl --vacuum-time=1seconds
journalctl --verify
echo "SystemMaxUse=64M" >> /etc/systemd/journald.conf
systemctl restart systemd-journald

6. tools

6.1. rrdtool on arm (raspberry)

vi /etc/yum.repos.d/xtras7.repo
#
[xtras7]
name=xtras7
baseurl=http://d01cid.ddns.net/sharel/img/xtras7-armv7hl/
enabled=1
gpgcheck=0
yum -y install rrdtool

7. logging

7.1. /var/log/ to ramdisk

curl -s http://d01cid.ddns.net/sharel/tar/log2ram.tgz | tar xzP -C /
/opt/log2ram/bin/install
cat /usr/lib/systemd/system/log2ram.service
[Unit]
Description=Log2Ram
DefaultDependencies=no
Before=basic.target rsyslog.service syslog.target systemd-journald.service sysinit.target shutdown.target apache2.service
After=local-fs.target
Conflicts=shutdown.target reboot.target halt.target
RequiresMountsFor=/var/log /var/hdd.log
IgnoreOnIsolate=yes

[Service]
Type=oneshot
ExecStart= /opt/log2ram/bin/log2ram start
ExecStop= /opt/log2ram/bin/log2ram stop
ExecReload= /opt/log2ram/bin/log2ram write
RemainAfterExit=yes

[Install]
WantedBy=sysinit.target
cat /bin/cid-hourly
#!/bin/sh
/bin/cid-ntp
/opt/log2ram/bin/log2ram "write"
systemctl enable log2ram.service
systemctl start log2ram.service

8. network

ss -4lpnt | grep slapd

9. wifi

yum -y install iw wireless-tools
ifconfig wlan0 up
iwlist wlan0 scan | grep ESSID
  or
iw dev wlan0 scan | grep SSID
iwconfig wlan0 essid d01s2
dhcpcd wlan0