Alice's questions

My machine abruptly report errors and immediately return to the Login Interface. (the errors are printed in the real terminal with cursor blinking too quick to capture a snapshot).

I re-log-in and check the syslog

$ head /var/log/syslog
May 13 05:22:54 alpha syslogd (GNU inetutils 1.9.4): restart
May 13 05:22:57 alpha vmunix: [22389.180680] IPv6: ADDRCONF(NETDEV_CHANGE): wlp3s0: link becomes ready
May 13 05:22:57 alpha vmunix: [22389.193601] xhci_hcd 0000:00:14.0: Timeout while waiting for setup device command
May 13 05:22:57 alpha dhclient[28475]: DHCPDISCOVER on wlp3s0 to 255.255.255.255 port 67 interval 3 (xid=0x607b5c72)
May 13 05:22:58 alpha dhclient[28475]: DHCPREQUEST of 192.168.31.117 on wlp3s0 to 255.255.255.255 port 67 (xid=0x725c7b60)

It prompt that GNU inetutils restart

$ last reboot | head -3
reboot   system boot  4.18.0-18-generi Sun May 12 08:12   still running
reboot   system boot  4.18.0-18-generi Sat May 11 19:35 - 00:00  (04:24)
reboot   system boot  4.18.0-18-generi Sat May 11 10:24 - 00:00  (13:35)

It shows that the machine did not reboot since yesterday

$ last | head -3 | sed "s/$USER/me/g"
me   :0           :0               Mon May 13 06:05   still logged in
me   :0           :0               Sun May 12 09:18 - 06:05  (20:46)
me   :0           :0               Sun May 12 09:09 - 09:18  (00:08)

but re-login at 06:15

The most recent x-session-error message before re-login

$ journalctl _UID=1000 --since '2019-05-13 07:30:00' --until '2019-05-13 08:12:00'  -r | cat
-- Logs begin at Sun 2019-03-17 07:29:49 CST, end at Mon 2019-05-13 17:18:51 CST. --
May 13 07:50:33 alpha /usr/lib/gdm3/gdm-x-session[8400]: (EE) client bug: timer event16 tap: offset negative (-286ms)
May 13 07:49:39 alpha /usr/lib/gdm3/gdm-x-session[8400]: (EE) client bug: timer event16 tap: offset negative (-35ms)
May 13 07:49:38 alpha /usr/lib/gdm3/gdm-x-session[8400]: (EE) client bug: timer event16 tap: offset negative (-31ms)
May 13 07:49:38 alpha /usr/lib/gdm3/gdm-x-session[8400]: (EE) client bug: timer event16 tap: offset negative (-275ms)
May 13 07:48:23 alpha org.gnome.SettingsDaemon.MediaKeys.desktop[8844]: # watch_established: "/org/gnome/terminal/legacy/" (establishing: 0)
May 13 07:48:23 alpha org.gnome.SettingsDaemon.MediaKeys.desktop[8844]: # unwatch_fast: "/org/gnome/terminal/legacy/" (active: 0, establishing: 1)
May 13 07:48:23 alpha org.gnome.SettingsDaemon.MediaKeys.desktop[8844]: # watch_fast: "/org/gnome/terminal/legacy/" (establishing: 0, active: 0)
May 13 07:48:22 alpha systemd[8325]: Started GNOME Terminal Server.
May 13 07:48:22 alpha systemd[8325]: Starting GNOME Terminal Server...
May 13 07:48:22 alpha systemd[8325]: This usually indicates unclean termination of a previous run, or service implementation deficiencies.
May 13 07:48:22 alpha systemd[8325]: gnome-terminal-server.service: Found left-over process 13165 (code) in control group while starting unit. Ignoring.
May 13 07:48:22 alpha systemd[8325]: This usually indicates unclean termination of a previous run, or service implementation deficiencies.
May 13 07:48:22 alpha systemd[8325]: gnome-terminal-server.service: Found left-over process 13157 (code) in control group while starting unit. Ignoring.
May 13 07:48:22 alpha systemd[8325]: This usually indicates unclean termination of a previous run, or service implementation deficiencies.

The detailed information about the machine:

The problem occurred two or three times daily which does interrupt the work routine.

I tried months but failed to take a picture when it report errors in a real terminal.

How could I fix the problem? or retrieve the errors from log?

The non-empty files /var/crash

$ ls -lS /var/crash
total 180376
-rw-r----- 1 gaowei   whoopsie 98063988 May  7 09:45 _usr_lib_xorg_Xorg.1000.crash
-rw-r----- 1 root     whoopsie 75786893 May 13 07:30 _usr_bin_emacs-gtk.0.crash
-rw-r----- 1 gaowei   whoopsie 10463542 May 12 08:25 _usr_share_code_code.1000.crash
-rw-r----- 1 gaowei   whoopsie   268660 May 11 15:35 _usr_bin_fcitx-dbus-watcher.1000.crash
-rw-r----- 1 gaowei   whoopsie   104470 May 13 07:24 _usr_bin_sogou-qimpanel.1000.crash
-rw-r--r-- 1 root     whoopsie        0 May 13 07:29 _usr_bin_emacs-gtk.0.upload

The most recent is _usr_share_code_code.1000.crash on 08:25 yesterday which uploaded as:

Ubuntu Pastebin

I want to check the time

Eastern Daylight Time Time zone in Washington, DC, USA (GMT-4) Thursday, May 9, 2019, 8:11 PM

However,

$ TZ="EDT" date
Fri May 10 00:12:25 EDT 2019

"EST" works properly

$ TZ="EST" date
Thu May  9 19:13:11 EST 2019

What's the problem?

With date -d could display the future or next date

$ date -d "next mon"
Mon May 13 00:00:00 CST 2019

$ date -d "mon"
Mon May 13 00:00:00 CST 2019

Unfortunately, it failed to display the previous weekday

$ date -d "previous Monday"
date: invalid date ‘previous Monday’

How could display the previous weekday in a string-format?

I have such a file with multiple blank lines in vscode

$ tail -n 20 draft3.py
            hi = len(a)  

        if lo < 0:
            raise ValueError('low must be non-negative')

        if lo == hi: 
            return None 

        mid = (lo + hi) // 2

        if x == a[mid]:
            return x
        if x > a[mid]:

            lo = mid + 1
            return self.bi_search(a, x, lo, hi)
        if x < a[mid]:

            hi = mid
            return self.bi_search(a, x, lo, hi)

Tried multiple methods to remove the blank lines

`grep -v -e '^$' failed

$ tail -n 20 draft3.py | grep -v -e '^$'
            hi = len(a)  
        if lo < 0:
            raise ValueError('low must be non-negative')
        if lo == hi: 
            return None 
        mid = (lo + hi) // 2

        if x == a[mid]:
            return x
        if x > a[mid]:

            lo = mid + 1
            return self.bi_search(a, x, lo, hi)
        if x < a[mid]:

            hi = mid
            return self.bi_search(a, x, lo, hi)

`grep -Ev "^$" failed

$ tail -n 20 draft3.py | grep -Ev "^$" 
            hi = len(a)  
        if lo < 0:
            raise ValueError('low must be non-negative')
        if lo == hi: 
            return None 
        mid = (lo + hi) // 2

        if x == a[mid]:
            return x
        if x > a[mid]:

            lo = mid + 1
            return self.bi_search(a, x, lo, hi)
        if x < a[mid]:

            hi = mid
            return self.bi_search(a, x, lo, hi)

`sed '/^$/d' failed

$ tail -n 20 draft3.py | sed '/^$/d'
            hi = len(a)  
        if lo < 0:
            raise ValueError('low must be non-negative')
        if lo == hi: 
            return None 
        mid = (lo + hi) // 2

        if x == a[mid]:
            return x
        if x > a[mid]:

            lo = mid + 1
            return self.bi_search(a, x, lo, hi)
        if x < a[mid]:

            hi = mid
            return self.bi_search(a, x, lo, hi)

What's the problem? How could remove the blank lines?

I learned from the question date - HH:MM:SS (with AM/PM) 12 Hour Timestamp for Bash Prompt - Unix & Linux Stack Exchange and fine-tune my prompt as:

export PS1='\D{%r}:\[\e]0;\u@\h: \w\a\]${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]:\n$ '
08:52:31 PM:me@host:~:
$

The time format is not very comfortable, the result I desire is

   08:52PM me@host~:

How could I get such a HH:MM(AM/PM) format\

The final result

export  PS1='\D{%I:%M%p %d/%m %A}:\[\e]0;\u@\h: \w\a\]${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]:\n$ '

10:45PM 18/03 Monday:me@host:~:

$ ls '$tty'

When I use htop, I found that an identical program occupies multiple lines:

Additionally the PID could not be traced:

me@host:~$ ps 16255 16256 16259 24772 16254
  PID TTY      STAT   TIME COMMAND

How could such an obscure happening?

I use apt-cache pkgname to retrieve the packages as

me@host:~$ apt-cache pkgnames | wc -l
62803

get 62803 results

but

me@host:~$ dpkg -l | wc -l
2336

What's the reasons which lead such a huge distinction. I presume that dpkg is super than apt.

I am reading a book with evince(version 3.30.1 on ubuntu 18.10) but find its notation function does not work properly

The source pdf file is in good quality because okular functions nicely.

I prefer the smooth design of evince than okular.

How could configure it to get a good annotation tool?

I tried to update the home directory to a backup computer as

rsync -avru --exclude-from='/home/me/exclude-me.txt' /home/me/* [email protected]:/home/assistant/* -p 2222

but get an error

Unexpected remote arg: [email protected]:
rsync error: syntax or usage error (code 1) at main.c(1361) [sender=3.1.2]

What's the problem with my codes?

I am very confused about the field X11DisplayOffset in sshd_config

Offset mean a position shift from the correct as lubuntu - Display offset. See image - Ask Ubuntu

However, when do ssh -X user@host to open 'firefox' on a remote desktop,
The Browser display correctly without offset.

What does X11DisplayOffset do?

Previously, I used sudo shutdown -h now to power off macOS. Upon powering on after this, the system would restore all the apps (like Chrome, VS Code, PDFs) to their previous status before shutdown.

Now, I used the same command sudo shutdown -h now to power off Ubuntu. But, upon powering on, the system starts an absolutely fresh state, without restoring the apps to their pre-shutdown state.

What's the functionality that macOS used? Can I use it on Ubuntu as well?

Upon reading GNU Core Utilities - Wikipedia, I find multiple sum

me@alpha:~$ cksum nohup.out 
4104911401 101860700 nohup.out
me@alpha:~$ b2sum nohup.out 
468c86394c5c4be04d0bce3b98584197b0c3f4cbb630144818f9d77d48ab7296e4c53db481b6bdd7c46dd5203d3f016d9ef01b126806e04be5003aeebb1bc6
22  nohup.out                                                                                                                
me@alpha:~$ sum nohup.out 
37767 99474
me@alpha:~$ sha1sum nohup.out 
79106925d593e18bd148ba94a6e4fb9da02e8c47  nohup.out
 me@alpha:~$ md5sum nohup.out 
3be4b17f18e4715d849a31ae482565cf  nohup.out

I started learning linux months ago, should I have to distinguish them and utilize them in daily operation?

Upon listing the blocks using lsblk, I found 14 look blocks listed, from loop 0 to loop 13.

me@alpha:~$ lsblk
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
loop0    7:0    0  87.9M  1 loop /snap/core/5662
loop1    7:1    0 140.7M  1 loop /snap/gnome-3-26-1604/74
loop2    7:2    0   3.7M  1 loop /snap/gnome-system-monitor/57
loop3    7:3    0 140.9M  1 loop /snap/gnome-3-26-1604/70
loop4    7:4    0  34.6M  1 loop /snap/gtk-common-themes/818
loop5    7:5    0  42.1M  1 loop /snap/gtk-common-themes/701
loop6    7:6    0  89.5M  1 loop /snap/core/6130
loop7    7:7    0   2.3M  1 loop /snap/gnome-calculator/238
loop8    7:8    0 130.2M  1 loop /snap/gnome-3-28-1804/4
loop9    7:9    0  14.5M  1 loop /snap/gnome-logs/45
loop10   7:10   0    13M  1 loop /snap/gnome-characters/124
loop11   7:11   0  53.7M  1 loop /snap/core18/536
loop12   7:12   0    13M  1 loop /snap/gnome-characters/139
loop13   7:13   0   2.3M  1 loop /snap/gnome-calculator/260
sda      8:0    0   113G  0 disk 
├─sda1   8:1    0   512M  0 part /boot/efi
└─sda2   8:2    0 112.5G  0 part /

However, when I list using ls /dev and find blocks using grep 'loop', I found 15 blocks listed, with an extra loop14 shown.

me@alpha:~$ ls /dev | grep 'loop'
loop0
loop1
loop10
loop11
loop12
loop13
loop14
loop2
loop3
loop4
loop5
loop6
loop7
loop8
loop9
loop-control

Why loop14 is not listed from lsblk?

When read /etc/resolv.conf:

me@alpha:~$ cat /etc/resolv.conf | tail -3                                                                                
# operation for /etc/resolv.conf.

nameserver 127.0.0.53

I got the idea of DNS from The Internet: IP Addresses & DNS - YouTube and aware that DNS is Google Public DNS - Wikipedia

How could the default namesever is a localhost address? I guess it impossible accessing to external services.

When tried the command

me@me:~$ ls -hl | head -5                                                                 
total 60M
-rw-r--r-- 1 me me  250 Jan 16 11:43 $tty
-rw-r--r-- 1 me me    0 Jan 16 11:41 1
drwxr-xr-x 2 me me 4.0K Jan 16 15:28 Desktop
drwxr-xr-x 7 me me 4.0K Jan 13 14:33 Documents

Found that Documents directory has 7 hard links, what's the reason for such a redundancy?

When I check the /var/log, I find something very strange

me@me:~$ ls -lt /var/log |head -6 '
total 160368
-rw-r-----  1 syslog            adm              19919118 Jan 15 16:55 auth.log
-rw-r-----  1 syslog            adm             139702302 Jan 15 16:55 syslog
-rw-r-----  1 syslog            adm                191122 Jan 15 16:55 mail.log
-rw-r-----  1 syslog            adm               2210432 Jan 15 16:32 kern.log
-rw-r--r--  1 root              root              1741863 Jan 15 14:22 dpkg.log

Notice that the owner of the first four log file is syslog. It's weird, because there is only one user on my system:

me@me~$ users
me

Why could a filename syslog be a user?

I have to machines running Ubuntu 18.10

When ssh -X to another computer

  ssh -X [email protected]

firefox and google-chrome could be opened at the current machine with firefox

firefox  
google-chrome

However, if tried to open the files manager with

xdg-open .
#or
nautilus .

the file manager is launched from the desktop of remote machine rather than the current.

I want to create a markdown file and open it simultaneously

$ touch ~/Documents/Ubuntu/drafts.md; open ~/Document/Ubuntu/drafts.md

The solution is cumbersome, is there a shortcut to handle such a task?

I’m trying to install gnutls but get an error message:

$ sudo apt install gnutls
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package gnutls

I take us.ubuntu as source in software update setting.

How to install gnutls properly?

I installed Ubuntu 18.10 yesterday, but I find myself missing some useful multitouch touchpad gestures.

In particular, I'd like to have a three finger drag gesture to move windows around.
On Ubuntu, you have to perform such a task with two hands, one to select the window and the other to drag around.

How could I implement this 3 finger gesture?