#acl merlyn:read,write All:read
#language zh-tw
<<TableOfContents()>>

= Linux TIPS =

== Convert UTF-16 ittle-endian text, with CRLF line terminators to UTF-8 ==
{{{
$ file HUA-MDS9148s-00_2021-11-12_8_43_28.log
HUA-MDS9148s-00_2021-11-12_8_43_28.log: Unicode text, UTF-16, little-endian text, with CRLF line terminators
 merlyn@brightmoon ~/Downloads
 $ iconv -f UTF-16LE -t UTF-8 HUA-MDS9148s-00_2021-11-12_8_43_28.log | head
[BEGIN] 2021/11/12 8:43:40
HUA-MDS9148s-00# show interface fc1/1,fc1/5,fc1/9,fc1/13
fc1/1 is up
    Port description is cnhuam0otc01-01-9a
    Hardware is Fibre Channel, SFP is short wave laser w/o OFC (SN)
    Port WWN is 20:01:00:3a:9c:68:21:10
    Admin port mode is auto, trunk mode is off
    snmp link state traps are enabled
    Port mode is F, FCID is 0x320100
    Port vsan is 100
}}}
== VLAN interface ==
{{{
ip link add link enp0s31f6 name eth0 type vlan id 2092
ip addr add 10.97.2.235/24 brd 10.97.2.255 dev eth0
ip link set dev eth0 up
}}}

== How to find WWN, WWNN and WWPN number of HBA card in Linux ==
{{{
cat /sys/class/fc_host/host*/port_name

systool -c fc_host -v | egrep "port_name|port_state|speed "
}}}

== Performance ==
https://cromwell-intl.com/open-source/performance-tuning/file-systems.html

== Diff, show modified line from right file only ==
diff --unchanged-line-format= --old-line-format= --new-line-format='%L' a b

== config RHEL services ==
{{{
service=(crond network ntpd rsyslog sshd sysstat irqbalance)
chkconfig --list | awk '{ print $1 }' | xargs -n1 -I@ chkconfig @ off
echo ${service[@]} | xargs -n1 | xargs -I@ chkconfig @ on
}}}

== Connecting a Bluetooth device for serial communication ==
{{{
rfcomm0 {
  # Automatically bind the device at startup
  bind no;
  # Bluetooth address of the device
  device 11:22:33:44:55:66;
  # RFCOMM channel for the connection
  channel 3;
  # Description of the connection
  comment "This is Device 1's serial port.";
}

Scan for bluetooth devices:

hcitool scan
Scanning ...
    20:15:12:08:62:95   HC-06

Bind using rfcomm

sudo rfcomm bind 0 20:15:12:08:62:95 1

NB: bind 0 refers to device number 0 (rfcomm0) and 1 is the channel. 
}}}


*    Pair using bluetoothctl:
{{{

    power on
    agent on
    scan on
    ... wait ...
    scan off
    pair <dev>

Create serial device: rfcomm bind 0 <dev>

You should now have /dev/rfcomm0.
}}}

== RAID ==
RAID 10

RAID 1+0 (or 10) is a mirrored data set (RAID 1) which is then striped (RAID 0), hence the "1+0" name. A RAID 1+0 array requires a minimum of four drives – two mirrored drives to hold half of the striped data, plus another two mirrored for the other half of the data. In Linux, MD RAID 10 is a non-nested RAID type like RAID 1 that only requires a minimum of two drives and may give read performance on the level of RAID 0.

RAID 01

RAID 0+1 (or 01) is a striped data set (RAID 0) which is then mirrored (RAID 1). A RAID 0+1 array requires a minimum of four drives: two to hold the striped data, plus another two to mirror the first pair.

== X11 putty ==
enable X11 Forward
  * then
[root@node1 ~]# export DISPLAY=:0

== How can I dual-boot Windows 10 and Linux ==
http://askubuntu.com/questions/666631/how-can-i-dual-boot-windows-10-and-ubuntu-on-a-uefi-hp-notebook

https://archives.gentoo.org/gentoo-user/message/a6c3d40e8827f65df098269e01186b59

http://unix.stackexchange.com/questions/316602/how-to-properly-dualboot-opensuse-and-windows-10


== Enter single usermode ==
rw init=/bin/bash

== Convert audio to text ==

==  how to export outlook exchange calendar to my google calendar ==
http://oregonstate.edu/helpdocs/faq/how-do-i-export-my-outlook-exchange-calendar-my-google-calendar
{{{
If you are on Windows PC: Open up your Microsoft Outlook program

If you are on a Mac OS X PC: Go to https://exmail.oregonstate.edu/owa

    Click on Calendar in the lower left corner
    You should see all your calendars in front of you. On the left side of the window, you should see the list of calendars and their names. Under My Calendars, right click the one you wish to add to your Google account.
    After right clicking your chosen calendar, right click, go Share > Publish This Calendar (Publish This Calendar to the Internet)
    A new window will pop up. Select the options for which best suit you. 
    When complete, press Start Publishing in the lower right corner.
    A couple of urls will show up for you to copy. Find the one that ends in .ics and copy that whole url.
    Go to Google Calendar
    When logged in to view your calendar, go find Other Calendars on the left side of the window
    After finding Other Calendars, there should be a box with a triangle in it to the right of the text. Click that box and find "Add by URL".
    A popup will show up. In this popup, you want insert the .ics URL from your Outlook here.
    Press Add Calendar below.

If you would like to stop publishing your calendar and no longer receive updates to your Google Calendar you can follow these directions:

http://oregonstate.edu/helpdocs/e-mail/exchange-outlook-oregonstateedu/publishing-exchange-calendars
}}}

== show bonding status ==
watch cat /proc/net/bonding/bond0

== mpv about ==
$ mpv --secondary-sid=2 --sub-file=tlf-jerrymaguire.bd.eng.srt --sub-file=tlf-jerrymaguire.cht.srt Jerry\ Maguire\ 1996\ 1080p\ BluRay\ x264\ AAC\ -\ Ozlem.mp4 

== How to change the output color of echo in Linux ==
https://stackoverflow.com/questions/5947742/how-to-change-the-output-color-of-echo-in-linux

== Sed & Awk About ==
=== How do I insert a space every four characters in a long line? ===
{{{
$ echo "foobarbazblargblurg" | fold -w4 | paste -sd' ' -
}}}
=== You can make a copy ===
  * of /etc/init.d before hand, or provide a suffix to sed's '-i'
{{{
# sed -i.bak -- '1s/runscript/openrc-run/' /etc/init.d/*
}}}

=== Extract File Basename Without Path and Extension in Bash ===
{{{
$ s=/the/path/foo.txt
$ echo ${s##*/}
foo.txt
$ s=${s##*/}
$ echo ${s%.txt}
foo
$ echo ${s%.*}
foo

fbname=$(basename "$1" .txt)
echo "$fbname"
}}}
=== Add a column to any position in a file in unix [using awk or sed] ===
 awk -v FS='|' -v OFS='|' '{$3=$3"|"4} 1' 1.txt

=== How to insert text before the first line of a file ===
  * I've been looking around sed command to add text into a file in a specific line. This works adding text after line 1:

sed '1 a\
  * Use sed's insert (i) option which will insert the text in the preceding line.

sed '1 i\



=== Sed delete dos CR/LF line ===
{{{
sed 's/.$//' file > out 
sed 's/\x0D$//' file > out
}}}

=== To remove all whitespace (including tabs) from left to first word ===
{{{
echo "     This is a test" | sed -e 's/^[ \t]*//'
sed  '/\#/d;/^$/d' /etc/nginx/nginx.conf
}}}

=== sed replace spaces with single space ===
{{{
sed -e "s/ \+/ /g;/^$/d" < ml.txt  > mll.txt
sed 's/ \{1,\}/ /g' 
}}}
[[http://superuser.com/questions/241018/how-to-replace-multiple-spaces-by-one-tab]]

=== remove all unwanted blank space then SORT it ===
{{{
sed 's/ /\n/g' < list  | sort
}}}

=== add/replace within <<<&>>> ===
{{{
# & replaces whatever matches with the given REGEXP.
$ sed 's@^.*$@<<<&>>>@g' path.txt
<<</usr/kbos/bin:/usr/local/bin:/usr/jbin/:/usr/bin:/usr/sas/bin>>>
<<</usr/local/sbin:/sbin:/bin/:/usr/sbin:/usr/bin:/opt/omni/bin:>>>
<<</opt/omni/lbin:/opt/omni/sbin:/root/bin>>>
$ sed 's@/usr/bin@&/local@g' path.txt
/usr/local/sbin:/sbin:/bin/:/usr/sbin:/usr/bin/local:/opt/omni/bin:
/opt/omni/lbin:/opt/omni/sbin:/root/bin
}}}

== Find About ==
=== 把找到的文件复制到另一个地方 ===
{{{
find /mnt/sda7/software_linux/ -name "*.exe" | xargs -i cp {} /home/ftp/incoming/
find /mnt/sda7/software_linux/ -name "*.exe" -exec cp '{}' /home/ftp/ ';'
find cacti-xxxx -type d -exec mkdir -p utf/{} ';'
find cacti-xxxx -type f -exec iconv -f GB2312 -t UTF-8 {} -o utf/{} ';'
find /home/user1 -name '*.txt' | xargs cp -av --target-directory=/home/backup/ --parents 
}}}

=== Find out all the jpg images and archive it ===
{{{
find /var/log -name '*.log' | tar cv --files-from=- | bzip2 -9 > log.tar.bz2 
find / -name *.jpg -type f -print | xargs tar -cvzf images.tar.gz
}}}

=== create symbol link from DIR ===
{{{
find /mnt/data/media/* -maxdepth 0 -type d -exec ln -sv '{}' . \;
}}}

=== 把目录下的包含大写字母的文件列出来 ===
{{{
find /usr/share/ -type f | xargs ls -l | grep '[:upper:]' | less -r
find . -maxdepth 2 -size +100M -exec ls -lh "{}" \;
}}}

=== 把目录下所有iso文件找出来并计算总大小(GB) ===
{{{
find /srv/ /mnt/media/ -name "*.iso" | xargs ls -lk | echo `awk '{a+=$5}END {print a}'`/1024/1024 | bc
find /srv/ /mnt/media/ -name "*.iso" | xargs ls -lk | awk '{a+=$5}END {print "Total sum is", a/1024/1024"GB"}'
find /srv/ /mnt/media/ -name "*.iso" -printf "%s\n" 2>/dev/null | awk '{a+=$1}END { print "Total sum is", a/1024/1024/1024"GB\nTotal time is :"}'
}}}

== Find files out then Copy files with sequence number ===
{{{
find . -name "*tgz" -type f -exec ls -Sr '{}' \; |awk '{system("cp -v "$0" "NR)}'
}}}

=== 查找20100401时更改过的文件 ===
{{{
cat >> 20100401.sh <<"EOF"
FILE=`find ./ -name "*.tex"`
ls -l --full-time $FILE 2>/dev/null
grep "2010-04-01"
EOF
}}}

== Niubility Tool Netcat ==
=== Transfer file(s) ===
 * Suppose you want to send files in /data from computer A with IP 192.168.2.111 to computer B(with any IP), It's as simple as this:
{{{
server: $ tar -cf - /data | nc -l -p 6666
client: $ nc 192.168.2.111 6666 | tar -xf -
}}}
 * A single file can be sent even easier.
{{{
server: $ cat file | nc -l -p 6666
client: $ nc 192.168.2.111 6666 > file
}}}
 * And you may copy and restore whole disk with nc:
{{{
server: $ cat /dev/sda | nc -l -p 6666
cliend: $ nc 192.168.2.111 6666 > /dev/sda
}}}

=== As Port Scanner ===
nc -vv -z 127.0.0.1 8079-8081

== history how to use ==
{{{
$ history | grep 'ipt'
2    iptables -L -n -v -t nat
}}}
$ !2     # will execute the iptables command
* MarkS, yes I know a way to make history contain only uniques. Do the following:
{{{
export HISTIGNORE="&"
That will make history not to save duplicate consecutive entries!
}}}

== some keycodes err will resolve ==
 * Added new keycodes for sk2506 HP multimedia 23-key keyboard
{{{
setkeycodes e016 235
setkeycodes e01e 158
setkeycodes e012 146
setkeycodes e014 148
setkeycodes e015 149
setkeycodes e02d 173
setkeycodes e018 236
setkeycodes e026 238
setkeycodes e017 227
setkeycodes e01f 159
setkeycodes e025 239
setkeycodes e023 237
}}}
=== For my HASEE-F4200  ===
{{{
atkbd.c: Unknown key released (translated set 2, code 0xd8 on isa0060/serio0).
atkbd.c: Use 'setkeycodes e058 <keycode>' to make it known.
getkeycodes will show you codes!
}}}
then
{{{
setkeycodes e058 125
}}}

== Safe Copying ==
{{{
#!/bin/bash
if [ -f $2 ]
then
	echo "$2 is exists. Do you want to overwrite it? (y/n)"
	read yn
	if [ $yn = "N" || $yn = "n" ]
	then
		exit 0
	fi
fi
cp $1 $2
}}}

== SMB About ==
{{{
mount.cifs //nas.systec.com.cn/Share /mnt/zip/ -o user=cml,domain=systec.com.cn

smbmount //192.168.2.51/D memory/ -o iocharset=cp936,user=xxxx,pass= --verbose
smbclient -U user -I 192.168.16.229 -L //smbshare/    # List the shares
mount -t smbfs -o username=winuser //smbserver/myshare /mnt/smbshare
mount -t cifs -o username=winuser,password=winpwd //192.168.16.229/myshare /mnt/share
sudo mount -t cifs -o username=${USER},password=${PASSWORD},uid=<user>,gid=<group> //server-address/folder /mount/path/on/ubuntu
[[http://unix.stackexchange.com/questions/68079/mount-cifs-network-drive-write-permissions-and-chown]]
}}}


== ss AND netstat && route && ip ==
 * This program is obsolete.  Replacement for netstat is ss.  Replacement for netstat -r is ip route.  Replacement  for  netstat  -i  is  ip  -s  link.Replacement for netstat -g is ip maddr.
{{{
ss -r
ip -s
ip maddr
netstat -lptu
netstat -antup
}}}

=== Add route gateway ===
{{{
route add a.b.c.d dev wlan0
ifconfig eth0 128.100.75.111 broadcast 128.100.75.0 netmask 255.255.255.0
route add -net 128.100.75.0 netmask 255.255.255.0
route add default gw 10.7.84.1 dev wlan0
}}}

=== two network card with gateway ===

/TwoNetworkCardWithGateway

== hdparm ==
{{{
hdparm -a 256 -d 1 -r 0 -u 0 -m 2 -c 1 -A 1 -K 0 -P 0 -X 0 -W 0 -S 0 /dev/sda 
}}}
will enable DMA ,32bit support, Sector count for multiple sector I/O to 2

==  If your swapdisk is less than a 1GB, then ==
{{{
dd if=/dev/zero of=/directory/with/much/free/space/tempswap bs=1k count=1000000
chmod 600 tempswap
mke2fs tempswap
mkswap tempswap
swapon tempswap
}}}



== Writing the actual CD ==

=== List content of ISO file ===
isoinfo -f -R -i cflinux-1.0.iso


 * Assuming that you've got cdrecord installed and configured for your cd-writer
type:
{{{
cdrecord --scanbus
cdrecord -v speed=<desired writing speed> dev=<path to your writers generic scsi device> boot.iso
}}}


== Sort about ==
 * Generate a tags file in case-insensitive sorted order.
{{{
find src -type f -print0 | sort -z -f | xargs -0 etags --append
}}}

Shuffle a list of directories, but preserve the order of files
within each directory.  For instance, one could use this to
generate a music playlist in which albums are shuffled but the
songs of each album are played in order.
{{{
ls */*.mp3 | sort -t / -k 1,1R -k 2,2
sort -n -k 2 -t : facebook.txt
sort: ls -l | sort -nr +4
cut: cut -f1 -d':' < /etc/passwd	
}}}

== Shuf about ==
{{{
shuf <<EOF
x
xx
xxx
EOF
shuf -i 1-100
shuf -e clubs hearts diamonds spades
}}}

== Paste about ==

 * For example
{{{
     $ cat num2
     1
     2
     $ cat let3
     a
     b
     c
     $ paste num2 let3
     1       a
     2       b
             c
$ paste -d '%_' num2 let3 num2
          1%a_1
          2%b_2
          %c_
}}}

== Join about ==
 * For example:
{{{

     $ cat file1
     a a1
     c c1
     b b1
     $ cat file2
     a a2
     c c2
     b b2
     $ join file1 file2
     a a1 a2
     c c1 c2
     b b1 b2
}}}

== What is "NR==FNR" in awk ==
{{{
 26
down vote
	

Look for keys (first word of line) in file2 that are also in file1.
Step 1: fill array a with the first words of file 1:

awk '{a[$1];}' file1

Step 2: Fill array a and ignore file 2 in the same command. For this check the total number of records until now with the number of the current input file.

awk 'NR==FNR{a[$1]}' file1 file2

Step 3: Ignore actions that might come after } when parsing file 1

awk 'NR==FNR{a[$1];next}' file1 file2 

Step 4: print key of file2 when found in the array a

awk 'NR==FNR{a[$1];next} $1 in a{print $1}' file1 file2
}}}


== urxvt run console application ==
{{{
urxvt -e bash -c geany_run_script.sh
urxvt -hold -e bash -c "./application"
}}}
https://bbs.archlinux.org/viewtopic.php?id=63516

== Wireless reject due to mismatch with WPA/WPA2 ==

== Convert png/jpeg to movie(mpeg,mpg,avi,gif) ==

convert -delay 10 -loop 0 *.png animation.gif

== Rename about ==
=== Upper to Lower Case ===
rename 'y/A-Z/a-z/' *.HTML

== 降低屏幕蓝光的小工具 ==
redshift

== app-crypt/letsencrypt ==
Let's Encrypt 是一个新的数字证书认证机构，它通过自动化的过程消除创建和安装证书的复杂性，为网站提供免费的 SSL/TLS 证书。

== celestia ==
实时太空模拟

== ssh about ==
 * Unable to negotiate with 192.168.0.195: no matching key exchange method found. Their offer: diffie-hellman-group1-sha1 
ssh -oKexAlgorithms=+diffie-hellman-group1-sha1   root@192.168.0.195

== Serial Monitor ==
socat /dev/ttyS0,raw,echo=0 SYSTEM:'tee input.txt | socat - "PTY,link=/tmp/ttyV0,raw,echo=0,waitslave" | tee output.txt'

screen /dev/tty.usbserial-blahblah 9600

== ALSA always on mute after startup ==
Disabling the module "module-device-restore" in /etc/pulse/default.pa solves the "mute" problem.

== tcpdump how to ==
https://forum.ivorde.com/tcpdump-how-to-to-capture-only-icmp-ping-echo-requests-t15191.html

https://danielmiessler.com/study/tcpdump/

== Reset Your Forgotten Linux Password in 2 Minutes or Less ==
Grub OR LILO +  rw init=/bin/bash

== parted ==
  * Command: mklabel label-type
{{{
Creates a new disk label, of type label-type. The new disk label will have no partitions. This command (normally) won’t technically destroy your data, but it will make it basically unusable, and you will need to use the rescue command (see Related information) to recover any partitions. Parted works on all partition tables. 1

label-type must be one of these supported disk labels:

    bsd
    loop (raw disk access)
    gpt
    mac
    msdos
    pc98
    sun 
}}}

How to align partitions for best performance using parted
{{{
parted /dev/sdb mkpart primary 0% 100%
parted /dev/sda mkpart oracle-data ext4 250GB 100%
parted /dev/sdb print
}}}

= Troubleshooting =
== sudo: sorry, you must have a tty to run sudo ==
No panic, there is an easy fix! tty. This is generally enforced by having Defaults requiretty in the /etc/sudoers.

To disable requiretty globally or to a single command, you have two options:

    Replace Defaults requiretty by Defaults !requiretty in your /etc/sudoers. This will impact your global sudo configuration.

Alternatively, you can change this configuration at a per user, per group or per command basis
{{{
Defaults!/path/to/my/bin !requiretty
Defaults:myuser !requiretty
}}}
    Connect by ssh using -t options

From man ssh:

     -t      Force pseudo-tty allocation.  This can be used to execute arbitrary screen-based programs on a remote
             machine, which can be very useful, e.g. when implementing menu services.  Multiple -t options force
             tty allocation, even if ssh has no local tty.


== Short tip: Removing orphaned SAN multipath devices under Enterprise Linux ==
  * https://access.redhat.com/solutions/47438
  * https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html-single/dm_multipath/#config_file_blacklist
  * https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/storage_administration_guide/removing_devices
{{{
# vi /etc/multipath.conf

# service multipathd reload

# multipath -l

After removing the LUN in the SAN backend, a unnamed LUN was added to the multipath topology. Removing this device was not possible as it seemed to be in use:

# multipath -f mpathf


To remove the dead device, the following commands needed to be executed:
# dmsetup remove -f mpathf
# multipath -f mpathf

}}}

== Change default network name (ens33) to “eth0” in Centos7/RHEL7 ==

  * net.ifnames=0 biosdevname=0
{{{
[root@dns-server-01 mnt]# cat /etc/default/grub 
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="rd.lvm.lv=ol/root rd.lvm.lv=ol/swap rhgb quiet net.ifnames=0 biosdevname=0
"
GRUB_DISABLE_RECOVERY="true"

}}}

{{{
[root@dns-server-01 mnt]# grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.10.0-327.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-327.el7.x86_64.img
Found linux image: /boot/vmlinuz-3.8.13-98.7.1.el7uek.x86_64
Found initrd image: /boot/initramfs-3.8.13-98.7.1.el7uek.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-3dd58864573848458a5b2f45438633d1
Found initrd image: /boot/initramfs-0-rescue-3dd58864573848458a5b2f45438633d1.img
done
}}}

== How to Remove a Dead Mulitpath Device without Reboot in CentOS/RHEL ==
  1. remove the device map and replace the table with one that fails all I/O.

  * For example:

# dmesetup remove -f 360060e80166bac0000016bac000000da

  1. remove the multipath device.

  * For example:

# multipath -f 360060e80166bac0000016bac000000da

  1. Verify the deletion of the dead multipath device.

# multipath -ll





==  Under what conditions should the 'start_udev' command be run?  ==
https://access.redhat.com/solutions/221243

  * We run start_udev as part of the storage allocation procedure that we have. It works, but it can be disruptive if an oracle DB instance is up and running (the listener interfaces briefly disappear). Our RH versions that we certified for SAN are 4u5, 4u8, 5.4 and 5.5.

  * Nobody should ever run start_udev, only rc.sysinit should call start_udev.

== udev How to get rid of or remove the multipath device without rebooting the server, rescanning the scsi bus, or restarting multipathd ==
https://access.redhat.com/solutions/3941?page=1

 How to rescan the SCSI bus to add or remove a SCSI device without rebooting the computer
{{{
     # multipath -f multipath-device
     # blockdev --flushbufs device
     # echo 1 >  /sys/block/device-name/device/delete
}}}


== fsck ==
{{{
Try: fsck -pvcf -- will force a verbose check for bad blocks and automatically repair. If you still have issues then your HDD might have physical problems.
}}}

== Possible Causes of Ethernet Errors ==
{{{
Collisions: Signifies when the NIC card detects itself and another server on the LAN attempting data transmissions at the same time. Collisions can be expected as a normal part of Ethernet operation and are typically below 0.1% of all frames sent. Higher error rates are likely to be caused by faulty NIC cards or poorly terminated cables.

Single Collisions: The Ethernet frame went through after only one collision

Multiple Collisions: The NIC had to attempt multiple times before successfully sending the frame due to collisions.

CRC Errors: Frames were sent but were corrupted in transit. The presence of CRC errors, but not many collisions usually is an indication of electrical noise. Make sure that you are using the correct type of cable, that the cabling is undamaged and that the connectors are securely fastened.

Frame Errors: An incorrect CRC and a non-integer number of bytes are received. This is usually the result of collisions or a bad Ethernet device.

FIFO and Overrun Errors: The number of times that the NIC was unable of handing data to its memory buffers because the data rate the capabilities of the hardware. This is usually a sign of excessive traffic.

Length Errors: The received frame length was less than or exceeded the Ethernet standard. This is most frequently due to incompatible duplex settings.

Carrier Errors: Errors are caused by the NIC card losing its link connection to the hub or switch. Check for faulty cabling or faulty interfaces on the NIC and networking equipment. 
}}}

== Resource temporarily unavailable ==
{{{
  Resolution

    Check /etc/security/limits.conf and all files in /etc/security/limits.d/ for the current setting of the nproc value
    Extend the nproc value. This can be done in /etc/security/limits.conf or in any file in a file in /etc/security/limits.d/.
    Example of /etc/security/limits.conf:
}}}
https://gerardnico.com/wiki/linux/limits.conf
{{{
   Example of /etc/security/limits.conf file

*               hard    nofile          65535
*               soft    nofile          4096
@student        hard    nproc           16384
@student        soft    nproc           2047

A soft limit is like a warning and hard limit is a real max limit. For example, following will prevent anyone in the student group from having more than 50 processes, and a warning will be given at 30 processes.

@student        hard    nproc           50
@student        soft    nproc           30
}}}


== References ==
http://www.tecmint.com/free-online-linux-learning-guide-for-beginners/

http://rainbow.chard.org/2013/01/30/how-to-align-partitions-for-best-performance-using-parted

== Shadowsocks ==
https://shadowsocks.be/9.html
https://suiyuanjian.com/139.html

== systemd disable servers ==
  * The correct command to totally disable a service is systemctl mask wpa_supplicant.service
systemctl mask wpa_supplicant.service