database design – Why if a transaction unlock a data item immediately after its final access of that data item, then serializability may not be ensured

The quote below is from Silberschatz’s Database System Concepts. It says if a transaction unlock a data item immediately after its final access of that data item, serializability may not be
ensured. Can you please explain why serializability may not be ensured?

Transaction Ti may unlock a data item that it had locked at some earlier point.
Note that a transaction must hold a lock on a data item as long as it accesses that
item. Moreover, it is not necessarily desirable for a transaction to unlock a data item
immediately after its final access of that data item, since serializability may not be
ensured.

networking – WiFi is connected but still cannot access internet

I have a fresh install of the current version of antiX (19.3)

The WiFi appears to be working, but I can’t connect to anything.

The WiFi wasn’t working after the install, so to start the WiFi I did this:

  1. I first unblocked the wifi:

rfkill unblock 0
2. I used “ceni” to set up the connnection (all I did was select the wifi option, then selected my wifi’s name and then entered the password)

Two small graphical monitors then appeared on the desktop (“wlan0” up and “wlan0” down) which seem to show ingoing and outgoing packets – that is why I think the connection is working.

However I cannot connect to anything (in a browser or using ssh). I also tried to set up the connection using Connman, but that didn’t seem to help.

What could be wrong?

I have included some diagnostic output below.

> lspci
00:00.0 Host bridge: Intel Corporation Mobile 4 Series Chipset Memory Controller Hub (rev 07)
00:02.0 VGA compatible controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 07)
00:02.1 Display controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 07)
00:1a.0 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #4 (rev 03)
00:1a.1 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #5 (rev 03)
00:1a.7 USB controller: Intel Corporation 82801I (ICH9 Family) USB2 EHCI Controller #2 (rev 03)
00:1b.0 Audio device: Intel Corporation 82801I (ICH9 Family) HD Audio Controller (rev 03)
00:1c.0 PCI bridge: Intel Corporation 82801I (ICH9 Family) PCI Express Port 1 (rev 03)
00:1c.1 PCI bridge: Intel Corporation 82801I (ICH9 Family) PCI Express Port 2 (rev 03)
00:1d.0 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #1 (rev 03)
00:1d.1 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #2 (rev 03)
00:1d.2 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #3 (rev 03)
00:1d.3 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #6 (rev 03)
00:1d.7 USB controller: Intel Corporation 82801I (ICH9 Family) USB2 EHCI Controller #1 (rev 03)
00:1e.0 PCI bridge: Intel Corporation 82801 Mobile PCI Bridge (rev 93)
00:1f.0 ISA bridge: Intel Corporation ICH9M LPC Interface Controller (rev 03)
00:1f.2 SATA controller: Intel Corporation 82801IBM/IEM (ICH9M/ICH9M-E) 4 port SATA Controller (AHCI mode) (rev 03)
00:1f.3 SMBus: Intel Corporation 82801I (ICH9 Family) SMBus Controller (rev 03)
00:1f.6 Signal processing controller: Intel Corporation 82801I (ICH9 Family) Thermal Subsystem (rev 03)
02:00.0 Ethernet controller: Qualcomm Atheros AR242x / AR542x Wireless Network Adapter (PCI-Express) (rev 01)
03:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8101/2/6E PCI Express Fast/Gigabit Ethernet controller (rev 02)

> ifconfig
eth0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether 00:23:8b:9c:03:94  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1  (Local Loopback)
        RX packets 377  bytes 24988 (24.4 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 377  bytes 24988 (24.4 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.0.165  netmask 255.255.255.0  broadcast 192.168.0.255
        inet6 2001:8003:64f5:2900:224:2cff:fe1b:afdf  prefixlen 64  scopeid 0x0<global>
        inet6 fe80::224:2cff:fe1b:afdf  prefixlen 64  scopeid 0x20<link>
        ether 00:24:2c:1b:af:df  txqueuelen 1000  (Ethernet)
        RX packets 81  bytes 6862 (6.7 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 111  bytes 18487 (18.0 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

> route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.0.1     0.0.0.0         UG    0      0        0 wlan0
192.168.0.0     0.0.0.0         255.255.255.0   U     0      0        0 wlan0

> ping -c 4 8.8.8.8
(no output - it just blocks)

> ping -c google.com
(no output - it just blocks)

> cat /etc/resolv.conf
# Generated by Connection Manager
nameserver ::1
nameserver 127.0.0.1

Cant access the site after I made a clone of Magento 2.3.5-p1 Instance using AMI on EC2

I would be really grateful if you can give me a solution to this.

  1. My main website is working fine on a custom domain "www.example.com". I made a clone of this using AMI and created a new instance on AWS.
  2. Now on the new instance(cloned) I cannot access the website I tried changing the base url to IP of the new instance and also to the localhost:8080. None of them appear to be working.
  3. I did run cache:flush and access rights to various directory (html,var,app,etc,pub,generated) non seems to be working

Please help, your input will be highly appreciated.

Regards.

wi fi – Is there an application or a method to test the positioning on Android only by wi fi access points?

I need to test positioning only by wi fi access points.But when I turn on geolocation on my Android device the position is calculated by GPS+ GSM + Wi fi. My device doesn’t give the option to save it and only determine by the wi fi networks.

So is there some way or application that will give such an opportunity to use only Wi Fi access points for positioning?

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encryption – MySQL Security – Is there an easy way to encrypt a confidential data and also that it cannot view or access by DBA?

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Can’t access my phone memory suddenly after using SD card as internal memory

A few weeks ago I integrated my SD card to use as phone memory. Everything was fine until a couple of days ago.

All of a sudden I saw the “insert SD card” notice appear on the notification bar. I open the back cover but the SD card looked like it was in place. I remove it and insert it back and the notice disappears. But then I notice that when I go to file explorer (FX) to access my files, it says “Access was denied”. I can’t access anything that is on my phone memory, although the apps are working. I guess system files are OK, but everything else is not.

My phone is rooted so I tried to access the files through TWRP but I can only see system folders.

Phone is a Moto C plus. Nougat.