Linux

Table of Contents

There's a separate page for some Installation related issues. A page about samba.

One of the most wired error I had (multiple times) is that, my dist is full. Then I cannot log into my account. Hopefully the home partition is separate from root partition, I can still log into root to discover this thing.

One of the situation I encountered is the xsession-errors file is more than 400G.

1 Network

To resolve a name to IP address, you can add it into /etc/hosts. E.g. at the end of the file, add: 

172.18.0.2 srcml-server-container

The scenario to use this is that host system cannot resolve the name of container to the specific IP. I have to specify it manually.

ifconfig is in net-tools package, and is deprecated. Use ip instead: 

ip addr show <dev>
ip link # show links
ip link show <dev>

2 Trouble Shooting

2.1 Cannot su root

When su cannot change to root, run 

chmod u+s /bin/su

2.2 in docker, cannot open chromium

failed to move to new namespace: PID namespaces supported, Network namespace supported, but failed: errno = Operation not permitted.

Solution 

chromium --no-sandbox

3 Files

In Unix, everything is a file.

/etc/X11/rgb.txt
rgb file

4 System

iostat
to monitor the IO usage. (from sysstat package)
id
show the group information of current user
dmesg
kernel log
/proc/cpuinfo
the file describing CPU
  • hostname -i: print host ip addr

5 Shell Interaction

Ctrl-s
stop the screen
Ctrl-q
recover the screen
Shift-pageup/down
page up & down
shift-Insert
paste
Ctrl-l
clear

6 App

  • File explorer: konquerer
  • Image viewer: feh

setting the wallpaper by: 

feh --bg-fill /path/to/wall/paper

And load previous setting by: 

sh ~/.fehbg &
  • image processing: graphicsmagick, imagemagick

6.1 Speech recognition engines

gnustep-gui-runtime
say "hello" It is not working yet
festival
echo "hello" | festival --tts The speech is pretty smooth
speech-dispatcher
spd-say "hello" quality is not that good
espeak
espeak "hello" quality is not that good

6.2 mplayer

Interactive controls:

LEFT/RIGHT
10 sec
UP/DOWN
1 min
PGUP/PGDWN
10 min
[]
playback speed by 10%
{}
half/double speed
BACKSPACE
reset playback speed
/*
volume
SPACE
pause
f
toggle fullscreen
o
OSD

When changing the speed, the pitch changed. To disable this, start mplayer by mplayer -af scaletempo.

To stretch the images to full screen, pass the -zoom option when starting.

6.3 unzip

  • -q: quiet
  • -d folder: output to that folder

Cannot rename the content, must mv after extraction.

6.4 youtube-dl

When downloading a playlist, you can make the template to number the files 

youtube-dl -o "%(playlist_index)s-%(title)s.%(ext)s" <playlist_link>

Download music only: 

youtube-dl --extract-audio --audio-format flac <url>

6.5 VNC

I use tigervnc because it seems to be fast.

  • vncpasswd: set the password
  • vncserver&: start the server.
    • It is started in :1 by default, so connect it with vncviewer <ip>:1
    • On mac, the docker bridge network does not work, so you cannot connect to the contianer by IP addr. In this case, map the port 5901. 5900+N is the default VNC port.
    • vncserver -kill :1 will kill the vncserver
    • vncserver :2 will open :2

6.6 mpd

music play daemon

To start: 

mkdir -p ~/.config/mpd
cp /usr/share/doc/mpd/mpdconf.example ~/.config/mpd/mpd.conf
mkdir ~/.mpd/playlists

# Required files
db_file            "~/.mpd/database"
log_file           "~/.mpd/log"

# Optional
music_directory    "~/music"
playlist_directory "~/.mpd/playlists"
pid_file           "~/.mpd/pid"
state_file         "~/.mpd/state"
sticker_file       "~/.mpd/sticker.sql"

# uncomment pulse audio section
audio_output {
	type		"pulse"
	name		"My Pulse Output"
}

Start mpd by: 

systemctl --user start mpd
systemctl --user enable mpd

6.6.1 Clients

  • gmpc
  • stumpwm contrib mpd

7 Prompt

  • prompt($PS1-4)
    • \d: date
    • \D{format}
    • \h: hostname
    • \H: full hostname
    • \t: time 24hour HH::MM::SS
    • \T: time 12hour HH::MM::SS
    • \@: time 12hour am/pm
    • \A: time 24hour HH::MM
    • \w: current working directory
    • \W: basename of $PWD

7.1 escape color

  • 1: bold
  • 4: underline
  • 30-37: black, red, green, yellow, blue, pink, cyan, white
  • 40-47: background
  • 90-97: light
  • 100-107: light background

example:

  • \033[1;4;32;45m
  • \e[32;45m
  • \e[0m

in PS1, use:

  • \[\033[32;45m\]

8 Job control

  • C-z to suspend.
    • top, then you can see the CPU usage and all process IDs. Simply press k and enter the PID can kill the process.
  • refer a job
    • %n: job number
    • %%: current job
    • %+: current job
    • %-: previous job
    • %: current job
    • %ce: the job "ce"
    • %?ce: the job, whose command has "ce"

Some commands:

jobs
list all background jobs
fg %1
continue it in foreground
bg %1
continue it in background
kill %1
kill the job (first)

9 Install fonts

  • OTF: OpenType
  • TTF: TrueType
  • EOT: Embedded Open Type
  • WOFF: Web Open Font Format

To install: 

cp *.otf ~/.fonts
sudo fc-cache
fc-list

10 Power management

No extra software needed! systmed can handle it, by acpid. The configure file is /etc/systemd/logind.conf. man logind.conf for details. 

HandlePowerKey=hibernate
HandleLidSwitch=suspend

hibernate will save to disk, while suspend save to ram. Both of them will resume to the current status.

11 Grub

11.1 Introduction

Use grub 2 instead of grub legacy. For a quick look at what they look like:

Grub Legacy boot/grub/menu.lst: 

title           Debian GNU/Linux
root            (hd0,2)
kernel          /vmlinuz root=/dev/hda3 ro
initrd          /initrd.img

Grub 2 /boot/grub/grub.cfg: 

menuentry "Debian GNU/Linux" {
        set root=(hd0,3)
        linux /vmlinuz root=/dev/hda3
        initrd /initrd.img
}

Note that the root is (hd0,2) in grub legacy vs. (hd0,3) in grub 2.

11.2 Grub 2

The menu configure file is located at /boot/grub/grub.cfg. It is generated by /usr/sbin/update-grub (8) using templates from /etc/grub.d/* and settings from /etc/default/grub.

12 Run level

Use debian as example distribution.

The default run level is 2, corresponding to /etc/rc2.d/XXX scripts. By default there's no difference between level 2 to 5.

12.1 Run level description

  • 0: halt
  • S: single user mode on boot
  • 1: single user mode, switched from multi-user mode
  • 2: multi-user mode
  • 3,4,5
  • 6: reboot
  • telinit(8) can change the run level dynamically.
  • runlevel(8) check current run level

Those scripts starts with "S" or "K" meaning start or stop sent to systemd utility. Those scripts are symbol linked to ../init.d/xxx.

13 LDLIBRARYPATH

On CentOS, the default LD_LIBRARY_PATH does not contains the /usr/local/lib. The consequence is the -lpugi and -lctags are not recognized because they are put in that directory. Set it, or edit /etc/ld.conf.d/local.conf and add the path. After that, run ldconf -v as root to update the database.

Also, the error:

Linux error while loading shared libraries: cannot open shared object file: No such file or directory

is also because the cache is not updated. So the solution is sudo ldconfig

14 Networking using NetworkManager

Install network-manager package, and:

Start the service 

systemctl enable NetworkManager

change /etc/NetworkManager$/NetworkManager.conf to: 

[ifupdown]
managed=true

restart 

systemctl restart NetworkManager

14.1 add a wifi connection

nmcli device wifi list
nmcli device wifi connect IASTATE
nmcli device wifi connect ID password pwd

15 Remove viewer

The lab machines are accessed via spice. The client for spice is virt-viewer. It can be installed through package manager. The actual client is called remote-viewer, which is shipped with virt-viewer. So the command to connect to the .vv file: remove-viewer console.vv.

16 File Management

16.1 Swap File

A swap file can also be used as swap memory. When doing linking, the ld might fail because of lack of memory.

Check the current swap: 

swapon -s

Create swap file: 

dd if=/dev/zero of=/path/to/extraswap bs=1M count=4096
mkswap /path/to/extraswap

swapon /path/to/extraswap
swapoff /path/to/extraswap

This will not be in effect after reboot. To automatically swap it on, in /etc/fstab 

/path/to/extraswap none swap sw 0 0

16.2 Back Up & Syncing

16.2.1 rsync

This commnad is used to sync from source to destination. It does not perform double way transfer. It decides a change if either of these happens:

  • size change
  • last-modified time

rsync [options] src dst

Available options

  • -v: verbose
  • -h: human readable message
  • -z: compress
  • -r: recursively
  • -a: archive mode: preserve symblic links, file permissions, timestamps
  • -e ssh: use ssh
  • --progress: show progress
  • --include <regex>
  • --exclude <regex>
  • --delete: DANGEROUS if dst has more than src, delete those on dst
  • --max-size='200k': set the size limit for each file
  • --dry-run: dry run

Commonly used options: vhzra dry-run

Remember to use a option, otherwise the dst will always have newer (thus different) timestamp, and you will do the copy all the time.

17 Drivers

I was installing drivers for my RX470 on Debian strench. The good news is it works out of box, I guess using xserver-xorg-video-amdgpu. However the temperature is 58 idle.

To fix that, I tried to install the newest driver, the amdgpu-pro. It does not support Debian officially, although I can modify the install script to pass the system test (it tests Ubuntu or steam). The installation script failed, but leaves me with the /var/opt/amdgpu-pro-local repo, which is also visible by apt. All the things can be removed by running amdgpu-pro-uninstall. Installing amdgpu-pro package will fail the machine, and you will not be able to log in again. The integrated graphic card would still work to log in and fix this but unless you have one, don't try it … Installing xserver-xorg-video-amdgpu-pro seems did gives me a temperature of 50, much better ..

Of course, the fan on the GPU is spinning all the time even if I use integrated graphic. The RGB lighting is not going to be customize-able.

18 Encoding

When converting MS windows format to unix format, you can use emacs and call set-buffer-file-coding-system and set to unix. Or you can use dos2unix, perhaps by 

find . -name *.java | xargs dos2unix

19 Kernel Developers

  • Linus Torvalds
  • Steve Rostedt
  • Sarah Sharp
  • Greg Kroah-Hartman
  • Alan Cox
  • Dave Jones
  • Jean Delvare
  • Arnd Bergmann
  • Herbert Xu
  • Arnd Bergmann
  • Jes Sorensen
  • Jonathan Corbet