Some useful things to know in Linux.

Dumped

dns_privacy.txt

public/free dns:
dns.quad9.net
9.9.9.9
149.112.112.112
2620:fe::fe
2620:fe::9
 
Recursive DNS Server Addresses and Features - Service based configuration:
 
Recommended: Malware Blocking, DNSSEC Validation (this is the most typical configuration)
 
IPv4
9.9.9.9
149.112.112.112
 
IPv6
2620:fe::fe
2620:fe::9
 
HTTPS
https://dns.quad9.net/dns-query
 
TLS
tls://dns.quad9.net
 
Secured w/ECS: Malware blocking, DNSSEC Validation, ECS enabled
 
IPv4
9.9.9.11
149.112.112.11
 
IPv6
2620:fe::11
2620:fe::fe:11
 
HTTPS
https://dns11.quad9.net/dns-query
 
TLS
tls://dns11.quad9.net
 
Unsecured: No Malware blocking, no DNSSEC validation (for experts only!)
 
IPv4
9.9.9.10
149.112.112.10
 
IPv6
2620:fe::10
2620:fe::fe:10
 
HTTPS
https://dns10.quad9.net/dns-query
 
TLS
tls://dns10.quad9.net

Note on using valgrind…

$ valgrind --leak-check=full --track-origins=yes --log-file=valgrind.rpt \
	./my1asm85 ../my1asm85/asm/monitor85.asm

$ valgrind --tool=memcheck --leak-check=full --track-origins=yes -s \
	./my1asm85 ../my1asm85/asm/monitor85.asm

To disable user login

# passwd -l username

To re-enable user login

# passwd -u username

OR,

To disable user login

# usermod -L -e 1 username

To re-enable user login

# usermod -U -e "" username

I prefer/use the first one.

List all hosts in *.local

$ avahi-browse -atr | grep hostname | sort -u

To display extended ASCII (which is a non-standard), use Western-IBM850 encoding (instead of the currently common UTF-8). The extended ASCII is actually great in drawing boxes in text mode.

To merge multiple PDFs (using pdftk):

pdftk $(ls *.pdf | sort) cat output ../output.pdf

Use xournal (or, maybe, xournalpp) to mark/sign - used export PDF to recreate PDF. If the created PDF is big (tends to be), import from LibreOffice Draw and re-export PDF.

Just found out about /proc/sys/vm/drop_caches kernel interface today. Need to look at this some time…

* clear page cache {flag:0x01}
# echo 1 > /proc/sys/vm/drop_caches
* clear dentries and inodes {flag:0x02}
# echo 2 > /proc/sys/vm/drop_caches
* can request simultaneously {flag:0x02|0x01}
# echo 3 > /proc/sys/vm/drop_caches 

Got this info from somewhere online - I just put it into a script.

Note: Create access to an IPad… requires ifuse and libimobiledevice-utils packages (tested on Devuan).

setup_dev_env

#!/bin/bash
 
# setup_dev_env
# - got this info from internet, i just put it in a script
# - should source this file :p
 
WORK_PATH=`pwd`
[ -d "$1" ] && WORK_PATH=`cd $1;pwd`
echo "-- Setup environment in ${WORK_PATH}"
 
MAKE_PATH=0
add_path()
{
	[ -d "$1" ] && PATH="$1":$PATH && MAKE_PATH=1
}
add_path ${WORK_PATH}/bin
add_path ${WORK_PATH}/sbin
add_path ${WORK_PATH}/usr/bin
add_path ${WORK_PATH}/usr/sbin
[ $MAKE_PATH -eq 0 ] &&
	echo "** No binary path found!" && exit 1
export PATH
 
MAKE_PATH=0
add_ldlib_path()
{
	if [ -d "$1" ] ; then
		[ -z "$LD_LIBRARY_PATH" ] &&
			LD_LIBRARY_PATH="$1" || LD_LIBRARY_PATH="$1":$LD_LIBRARY_PATH
		MAKE_PATH=1
	fi
}
add_ldlib_path ${WORK_PATH}/lib
add_ldlib_path ${WORK_PATH}/usr/lib
[ $MAKE_PATH -ne 0 ] && export LD_LIBRARY_PATH
 
MAKE_PATH=0
add_c_path()
{
	if [ -d "$1" ] ; then
		[ -z "$CPATH" ] &&
			CPATH="$1" || CPATH="$1":$CPATH
		MAKE_PATH=1
	fi
}
add_c_path ${WORK_PATH}/include
add_c_path ${WORK_PATH}/usr/include
[ $MAKE_PATH -ne 0 ] && export CPATH
 
MAKE_PATH=0
add_man_path()
{
	if [ -d "$1" ] ; then
		[ -z "$MANPATH" ] &&
			MANPATH="$1" || MANPATH="$1":$MANPATH
		MAKE_PATH=1
	fi
}
add_man_path ${WORK_PATH}/share/man
add_man_path ${WORK_PATH}/usr/share/man
[ $MAKE_PATH -ne 0 ] && export MANPATH
 
MAKE_PATH=0
add_pkgcfg_path()
{
	if [ -d "$1" ] ; then
		[ -z "$PKG_CONFIG_PATH" ] &&
			PKG_CONFIG_PATH="$1" || PKG_CONFIG_PATH="$1":$PKG_CONFIG_PATH
		MAKE_PATH=1
	fi
}
add_pkgcfg_path ${WORK_PATH}/lib/pkgconfig
add_pkgcfg_path ${WORK_PATH}/usr/lib/pkgconfig
[ $MAKE_PATH -ne 0 ] && export PKG_CONFIG_PATH

I have Slackware 14.2 on my HP laptop, which has an RTL8723DE wifi module hardware. This module is still not supported in the mainstream kernel, but the driver is available at https://github.com/lwfinger/rtlwifi_new.git.

• get source, go extended

  $ git clone https://github.com/lwfinger/rtlwifi_new.git
  $ cd rtlwifi_new
  $ git checkout extended

• to install (as root)

  $ make install
  $ modprobe rtl8723de

• to uninstall module (e.g. for kernel update)

  $ rmmod rtl8723de
  $ make uninstall

• to get better signal strength, create file '/etc/modprobe.d/rtl8723de.conf' with:

  options rtl8723de ant_sel=2

Update20200824 That repo is no longer available. Using rtw88 instead (module is now named rtw88_8723de). Just to note that the rtw88 code is now in mainline kernel starting 5.2

Somehow, /dev/kvm is missing?? So, just create this udev rule:

65-kvm.rules

KERNEL=="kvm", GROUP="users", MODE="0660"
KERNEL=="vhost-net", GROUP="users", MODE="0660"

I mostly use sed / grep / cut for this. But I have found the need to use tr at times.

For example, to filter out non-ASCII characters

tr -cd '\000-\177'

When installing using extlinux, the file ldlinux.sys is created and cannot be removed even by root! The command chattr can be used to remove the flag that protects that particular file

# chattr -i ldlinux.sys

To check/confirm, run

# lsattr ldlinux.sys

After that, the file can be removed by root as usual.

Running my GUI code compiled with GTK3 on Artix causes a runtime warning message

dbind-WARNING **: 11:12:11.208: Couldn't register with accessibility bus: Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.

I found this simple fix somewhere in a forum - simply create an environment variable

export NO_AT_BRIDGE=1

$ xdpyinfo
$ xrdb -query

Note to self: CHECK THIS OUT! For example, on T23 laptop

$ hdparm -q -d1 -c3 -W1 -u1 -m 16 /dev/hda
$ hdparm -q -d1 -c3 -X66 /dev/hdc

1. xorg.conf, "mkfontscale", "mkfontdir", "ttmkfdir" => old school, nobody needs them?
2. /etc/fonts/*, ~/.fonts.conf, fc-cache, fc-list => the way to go

$ strip --strip-debug /lib/*
$ strip --strip-unneeded /{,s}bin/*

$ diff -Naur [file1] [file2] > file.patch
**Note**
  %%{{{@@ -X,Y +J,K @@}}}%% is a hunk where diff is
    X & J - starting line number
    Y & K - line counts

create_users

#!/bin/bash
 
USERLIST="$1"
 
[ ! -f "$USERLIST" ] &&
	echo "Cannot access user list '$USERLIST'! Abort!" && exit 1
 
# assume format is user:pass
for userpass in `cat $USERLIST` ; do
	user=`echo $userpass | sed 's/\([^:]\):.*/\1/'`
	pass=`echo $userpass | sed 's/.*:\(.*\)/\1/'`
	what=`echo $userpass | sed 's/^\(#\)[^#]*/\1/'`
	[ "$what" == "#" ] && continue
	what=`cat /etc/passwd | grep "$user"`
	[ "$what" != "" ] && continue
	echo "User:[$user],Pass:[$pass]"
	echo "${user}:${pass}::100:User Account:/home/${user}:/bin/bash"
done

By default, date/time are set manually: e.g. as root,

ntpdate pool.ntp.org

If ntpdate is not available (being deprecated?), use ntp daemon:

ntpd -gq

(May have to stop running ntp daemon)

For Slackware, a startup script for NTP daemon is available /etc/rc.d/rc.ntpd, but do not forget to modify /etc/ntp.conf and uncomment (or add custom) NTP server information. To query, use

ntpq -p

To still use ntpdate while NTP daemon is running, use the -d switch,

ntpdate -d pool.ntp.org

To display active pertitions,

cat /proc/partitions

To display cpu information,

cat /proc/cpuinfo

To check for Intel-VT virtualization features,

grep --color vmx /proc/cpuinfo

To check for AMD-V virtualization features,

grep --color svm /proc/cpuinfo

Note: Some BIOS may disable this feature by default. Also, old Linux kernel may not support it either.

To display memory information,

cat /proc/meminfo

To check shared libraries used by a program

cat /proc/<proc_id>/maps

I want to have LDAP-based central authentication for my two new Slackware machines used for my GMC project. Things to do:

1. get LDAP server installed and running
   • Slackware only have openldap-client by default
   • I'm referring to here to do this
2. figure out how to setup the client side
   • I may need nss_ldap only - will check into this later

On server, edit /etc/ssh/sshd_config

AllowTcpForwarding yes
X11Forwarding yes
X11DisplayOffset 10
X11UseLocalhost yes

On client, edit /etc/ssh/ssh_config

ForwardAgent yes
ForwardX11 yes

To connect,

# allow remote access for display
ssh -Y user@host
export DISPLAY=localhost:10.0
# then, run any x-program

Only the user on the main console gets control of display protocol. If we do su, the root user cannot use any GUI.

To disable and enable access control

$ xhost +
$ xhost -

Find and set DISPLAY value accordingly

$ echo $DISPLAY
$ export DISPLAY=:0.0

This enables us to have GUI access on a remote machine. I use screen because I want to keep the running terminal 'alive'.

Use virtual terminal, run screen on the remote machine

$ screen -S VNC

Start VNC server on a display port

$ vncserver :23

Note ~/.vnc/xstartup will be executed

To stop the VNC server

$ vncserver -kill :23

Detach the virtual terminal by hitting <CTRL+A>-<D>. To resume the virtual terminal from any console

$ screen -r VNC

To tunnel through SSH, start an ssh session (with port forwarding [5900+DP] and going background)

ssh -L 5923:localhost:5923 -N -f user@remotehost

Connect as if the server is on localhost

vncviewer localhost:23

Note: Desktop response becomes too slow for me! Not using this…

On Linux, multi-tasking is also available on console. To suspend a task, hit ctrl+z

To list all jobs duh!

$ jobs

To resume

$ fg %<num>

Rebuild VirtualBox kernel module

After a kernel upgrade… do a

# /etc/init.d/vboxdrv setup

Virtual Serial Port

We can actually use minicom to connect…

minicom -D unix\#/tmp/xxx

where /tmp/xxx is the host pipe

Convert Image to Disk

VBoxManage convertfromraw -format VDI <file.img> <file.vdi>

Compact Disk Image

VBoxManage modifymedium --compact <file.vdi>

Create Disk Image

VBoxManage createmedium disk --filename <file.vdi> --size <megabytes>

v4l2-ctl --list-devices
v4l2-ctl -d 0 --list-formats-ext
v4l2-ctl -d 0 --list-ctrls

v4l2-ctl --device=0 --set-ctrl=?

v4l2-ctl -d 0 --set-fmt-video=width=1920,height=1080,pixelformat=YUYV

Note At the moment, only read-only access (no write permission)!

# mount -t ufs -o ufstype=ufs2 /dev/<partition> <mount-path>

dokuwiki2github.sh

#!/bin/bash
 
DOKUWIKI=${DOKUWIKI:="$HOME/public_html/dokuwiki"}
WIKIPAGE=${WIKIPAGE:="$DOKUWIKI/data/pages"}
 
cd ${WIKIPAGE} && git add . && git add -u &&
	git commit -a -m "Content update `date +'%H:%M %d/%m/%Y %Z'`" &&
	git push origin master
 
# setup a cron job for hourly update:
#
# 0 * * * * dokuwiki2github.sh

Tested this on Slackware 14.2.

Using patch found here, I modified it a bit for latest Linux kernel used in Slackware 14.2 (4.4.190)

To create this patch, I copied out ch341.c from kernel source to my user path. Make another copy as ch341_patched.c. Modify as required. Do,

$ diff -u ch341.c ch341_patched.c > linux_4.4.190_ch341.patch

I do not know if this last step is needed, but I modified the patch so that the first two lines have the same file name.

linux_4.4.190_ch341.patch

--- ch341.c	2019-10-24 15:02:10.039646991 +0800
+++ ch341.c	2019-10-24 15:06:14.244416258 +0800
@@ -358,6 +358,7 @@
 	struct ch341_private *priv = usb_get_serial_port_data(port);
 	unsigned baud_rate;
 	unsigned long flags;
+	unsigned int par_flags;
 
 	baud_rate = tty_get_baud_rate(tty);
 
@@ -371,6 +372,30 @@
 	 * (cflag & PARENB) : parity {NONE, EVEN, ODD}
 	 * (cflag & CSTOPB) : stop bits [1, 2]
 	 */
+	/* CH340 doesn't appear to support variable stop bits or data bits */
+	if (C_PARENB(tty)) {
+		if (C_PARODD(tty)) {
+			if (tty->termios.c_cflag & CMSPAR) {
+				dev_dbg(&port->dev, "parity = mark\n");
+				par_flags = 0xeb;
+			} else {
+				dev_dbg(&port->dev, "parity = odd\n");
+				par_flags = 0xcb;
+			}
+		} else {
+			if (tty->termios.c_cflag & CMSPAR) {
+				dev_dbg(&port->dev, "parity = space\n");
+				par_flags = 0xfb;
+			} else {
+				dev_dbg(&port->dev, "parity = even\n");
+				par_flags = 0xdb;
+			}
+		}
+	} else {
+		dev_dbg(&port->dev, "parity = none\n");
+	par_flags = 0xc3;
+	}
+	ch341_control_out(port->serial->dev, 0x9a, 0x2518, par_flags);
 
 	spin_lock_irqsave(&priv->lock, flags);
 	if (C_BAUD(tty) == B0)

Steps (as root) in terminal:

1. get to location

   $ cd /usr/src/linux/drivers/usb/serial

2. patch ch341.c

   $ patch < /path/to/linux_4.4.190_ch341.patch

   • path/to is the path where you save the above patch
3. get to top kernel source path

   $ cd /usr/src/linux

4. compile module

   $ make M=drivers/usb/serial modules

5. (OPTIONAL) remove previously loaded module

   $ rmmod ch341

6. 'install' the module

   $ cp drivers/usb/serial/ch341.ko /lib/modules/`uname -r`/kernel/drivers/usb/serial/