How Many Usb Cameras Can I Connect To Raspberry Pi

Using Linux

Concluding

The terminal (or 'command-line') on a computer allows a user a peachy deal of control over their organization. Users of Windows may already take come across Command Prompt or Powershell, while mac Os users may exist familiar with Final. All of these tools allow a user to directly dispense their system through the use of commands. These commands tin be chained together and/or combined together into complex scripts that can potentially complete tasks more efficiently than much larger traditional software packages.

Opening a Terminal window

On the Raspberry Pi OS, the default final application is called LXTerminal. This is known equally a 'final emulator', this means that it emulates the old manner video terminals — from before Windowing systems were developed — inside a graphical environs. The awarding can exist establish on the Raspberry Pi desktop, and when started will look something like this:

Terminal screenshot

In the terminal window you should be able to encounter the following prompt:

This shows your username and the hostname of the Raspberry Pi. Here the username is pi and the hostname is raspberrypi.

Navigating and browsing your Raspberry Pi

One of the central aspects of using a terminal is being able to navigate your file system. Go ahead and blazon ls -la into the Terminal window, and then hit the Render key. Yous should see something like to:

ls result

The ls command lists the contents of the directory that you are currently in (your present working directory). The -la component of the control is what's known as a 'flag'. Flags change the command that'south being run. In this instance the l displays the contents of the directory in a list, showing data such as their sizes and when they were last edited, and the a displays all files, including those beginning with a ., known every bit 'dotfiles'. Dotfiles normally act as configuration files for software and as they are written in text, they can be modified by simply editing them.

In club to navigate to other directories the change directory control, cd, can be used. Yous can specify the directory that you lot want to go to by either the 'absolute' or the 'relative' path. So if you wanted to navigate to the python_games directory, you could either practise cd /dwelling/pi/python_games or just cd python_games (if you lot are currently in /home/pi). At that place are some special cases that may exist useful: ~ acts every bit an alias for your domicile directory, so ~/python_games is the aforementioned as /habitation/pi/python_games; . and .. are aliases for the current directory and the parent directory respectively, e.g. if y'all were in /abode/pi/python_games, cd .. would accept you to /habitation/pi.

History and car-consummate

Rather than type every command, the terminal allows you to coil through previous commands that you've run past pressing the upwards or downward keys on your keyboard. If you are writing the proper noun of a file or directory as part of a control then pressing tab will attempt to automobile-complete the name of what y'all are typing. For example, if you take a file in a directory called aLongFileName and then pressing tab after typing a will allow yous to choose from all file and directory names outset with a in the current directory, assuasive you lot to choose aLongFileName.

The `sudo` control

Some commands that brand permanent changes to the state of your system require you to have root privileges to run. The control sudo temporarily gives your account (if you're not already logged in every bit root) the ability to run these commands, provided your user proper name is in a list of users ('sudoers'). When y'all append sudo to the start of a command and printing enter, the command post-obit sudo will be run using root privileges. Be very conscientious: commands requiring root privileges tin irreparably damage your arrangement! Note that on some systems you will be prompted to enter your password when you run a command with sudo.

Further information on sudo and the root user tin be establish on the linux root page.

Installing software using `apt`

You can utilise the apt command to install software in Raspberry Pi Bone. This is the 'package manager' that is included with any Debian-based Linux distributions, including Raspberry Pi OS. It allows you to install and manage new software packages on your Raspberry Pi.

In order to install a new parcel, you would type sudo apt install <packet-name>, where <package-name> is the package that you desire to install.

Running sudo apt update will update a list of software packages that are bachelor on your system. If a new version of a parcel is available, then sudo apt full-upgrade volition update any old packages to the new version.

Finally, sudo apt remove <package-name> removes or uninstalls a package from your organisation.

Other useful commands

There are a few other commands that you may find useful, these are listed below:

cp makes a copy of a file and places it at the specified location (essentially doing a 're-create-paste'), for example - cp file_a /home/other_user/ would copy the file file_a from your habitation directory to that of the user other_user (assuming you take permission to re-create it there). Note that if the target is a binder, the filename will remain the aforementioned, but if the target is a filename, information technology volition requite the file the new proper noun.
mv moves a file and places information technology at the specified location (and then where cp performs a 're-create-paste', mv performs a 'cutting-paste'). The usage is similar to cp, and then mv file_a /home/other_user/ would motility the file file_a from your habitation directory to that of the specified user. mv is also used to rename a file, i.east. movement it to a new location, e.g. mv hullo.txt story.txt.
rm removes the specified file (or directory when used with -r). Warning: Files deleted in this way are mostly non restorable.
mkdir: This makes a new directory, e.g. mkdir new_dir would create the directory new_dir in the present working directory.
cat lists the contents of files, e.g. true cat some_file will display the contents of some_file.

Other commands you lot may discover useful can be found in the commands page.

Finding out most a command

To find out more than information nigh a particular command and then you can run the man followed past the command you desire to know more about (east.g. human being ls). The man-page (or manual page) for that command will exist displayed, including data almost the flags for that program and what effect they have. Some human-pages will give example usage.

The Linux File System

Information technology is important to have a basic understanding of the fundamentals of the Linux file system: where your files are kept, where software is installed, where the danger zones are, and then on. For more information, delight refer to the Linux Filesystem Hierarchy Standard.

Home

When you log into a Raspberry Pi and open up a terminal window, or you lot boot to the control line instead of the graphical user interface, you lot start in your domicile folder; this is located at /dwelling house/pi, assuming your username is pi.

This is where the user's ain files are kept. The contents of the user's desktop is in a directory here chosen Desktop, along with other files and folders.

To navigate to your home folder on the command line, simply blazon cd and printing Enter. This is the equivalent of typing cd /home/pi, where pi is your username. Yous can as well apply the tilde key (~), for example cd ~, which can be used to relatively link back to your home folder. For instance, cd ~/Desktop/ is the same as cd /home/pi/Desktop.

Navigate to /abode/ and run ls, and you lot'll see the home folders of each of the users on the system.

Annotation that if logged in equally the root user, typing cd or cd ~ will have you to the root user's home directory; unlike normal users, this is located at /root/ non /home/root/.

Linux Commands

Here are some fundamental and mutual Linux commands with example usage:

Filesystem

ls

The ls control lists the content of the current directory (or ane that is specified). Information technology tin be used with the -fifty flag to display additional information (permissions, owner, grouping, size, engagement and timestamp of concluding edit) near each file and directory in a list format. The -a flag allows yous to view files beginning with . (i.e. dotfiles).

cd

Using cd changes the current directory to the ane specified. Y'all can use relative (i.east. cd directoryA) or absolute (i.e. cd /abode/pi/directoryA) paths.

pwd

The pwd command displays the proper noun of the present working directory: on a Raspberry Pi, inbound pwd volition output something like /home/pi.

mkdir

Y'all can use mkdir to create a new directory, east.grand. mkdir newDir would create the directory newDir in the present working directory.

rmdir

To remove empty directories, utilise rmdir. So, for example, rmdir oldDir volition remove the directory oldDir simply if it is empty.

rm

The command rm removes the specified file (or recursively from a directory when used with -r). Be careful with this control: files deleted in this mode are mostly gone for expert!

cp

Using cp makes a copy of a file and places it at the specified location (this is similar to copying and pasting). For example, cp ~/fileA /home/otherUser/ would copy the file fileA from your home directory to that of the user otherUser (bold y'all accept permission to copy it there). This command can either take FILE FILE (cp fileA fileB), FILE DIR (cp fileA /directoryB/) or -r DIR DIR (which recursively copies the contents of directories) as arguments.

mv

The mv control moves a file and places it at the specified location (so where cp performs a 'copy-paste', mv performs a 'cutting-paste'). The usage is similar to cp. And so mv ~/fileA /home/otherUser/ would motion the file fileA from your domicile directory to that of the user otherUser. This command can either have FILE FILE (mv fileA fileB), FILE DIR (mv fileA /directoryB/) or DIR DIR (mv /directoryB /directoryC) as arguments. This control is too useful as a method to rename files and directories subsequently they've been created.

touch

The control impact sets the last modified time-stamp of the specified file(south) or creates it if information technology does not already exist.

cat

You lot can utilise true cat to listing the contents of file(due south), due east.g. cat thisFile will display the contents of thisFile. Can exist used to list the contents of multiple files, i.due east. cat *.txt volition listing the contents of all .txt files in the current directory.

head

The head command displays the offset of a file. Can be used with -n to specify the number of lines to show (by default ten), or with -c to specify the number of bytes.

tail

The contrary of head, tail displays the end of a file. The starting point in the file can be specified either through -b for 512 byte blocks, -c for bytes, or -due north for number of lines.

chmod

You lot would ordinarily utilise chmod to change the permissions for a file. The chmod control can use symbols u (user that owns the file), g (the files group) , and o (other users) and the permissions r (read), w (write), and x (execute). Using chmod u+x filename will add execute permission for the owner of the file.

chown

The chown command changes the user and/or group that owns a file. It commonly needs to be run every bit root using sudo due east.grand. sudo chown pi:root filename will modify the owner to pi and the group to root.

ssh

ssh denotes the secure shell. Connect to another computer using an encrypted network connection. For more than details see SSH (secure beat)

scp

The scp control copies a file from ane computer to another using ssh. For more details see SCP (secure copy)

sudo

The sudo command enables you to run a command equally a superuser, or some other user. Employ sudo -s for a superuser shell. For more details see Root user / sudo

dd

The dd control copies a file converting the file as specified. It is often used to re-create an unabridged disk to a single file or back over again. So, for instance, dd if=/dev/sdd of=backup.img will create a fill-in image from an SD card or USB disk drive at /dev/sdd. Brand certain to employ the correct drive when copying an prototype to the SD card as it tin can overwrite the entire disk.

df

Utilize df to display the disk space available and used on the mounted filesystems. Use df -h to meet the output in a human-readable format using Chiliad for MBs rather than showing number of bytes.

unzip

The unzip command extracts the files from a compressed zero file.

tar

Use tar to store or extract files from a record archive file. It can too reduce the infinite required by compressing the file similar to a nothing file.

To create a compressed file, use tar -cvzf filename.tar.gz directory/ To extract the contents of a file, use tar -xvzf filename.tar.gz

pipes

A piping allows the output from one control to be used as the input for another control. The pipe symbol is a vertical line |. For example, to only show the first 10 entries of the ls command information technology can be piped through the caput control ls | caput

tree

Use the tree command to show a directory and all subdirectories and files indented as a tree structure.

&

Run a command in the background with &, freeing up the shell for future commands.

wget

Download a file from the web directly to the figurer with wget. So wget https://datasheets.raspberrypi.com/rpi4/raspberry-pi-iv-datasheet.pdf volition download the Raspberry Pi 4 datasheet and salvage it every bit raspberry-pi-four-datasheet.pdf.

curl

Use curl to download or upload a file to/from a server. By default, it volition output the file contents of the file to the screen.

man

Testify the manual page for a file with man. To find out more, run man human to view the manual page of the human control.

Search

grep

Apply grep to search inside files for sure search patterns. For example, grep "search" *.txt volition look in all the files in the electric current directory catastrophe with .txt for the string search.

The grep command supports regular expressions which allows special letter combinations to exist included in the search.

awk

awk is a programming language useful for searching and manipulating text files.

find

The find control searches a directory and subdirectories for files matching certain patterns.

whereis

Use whereis to find the location of a command. Information technology looks through standard program locations until it finds the requested command.

Networking

ping

The ping utility is commonly used to check if communication can exist made with another host. It can be used with default settings by just specifying a hostname (e.g. ping raspberrypi.com) or an IP accost (east.g. ping 8.8.viii.8). It can specify the number of packets to send with the -c flag.

nmap

nmap is a network exploration and scanning tool. Information technology can return port and OS data about a host or a range of hosts. Running just nmap will display the options available also as example usage.

hostname

The hostname control displays the current hostname of the system. A privileged (super) user tin set the hostname to a new one past supplying information technology every bit an argument (e.g. hostname new-host).

ifconfig

Use ifconfig to display the network configuration details for the interfaces on the electric current organization when run without any arguments (i.eastward. ifconfig). By supplying the control with the name of an interface (e.g. eth0 or lo) you can and then alter the configuration: cheque the manual page for more than details.

Text Editors

On Linux, y'all take a choice of text editors. Some are easy-to-employ just take limited functionality; others require grooming to use and have a long time to master, only offer incredible functionality.

Text Editors on Desktop

Text Editor

When using Raspberry Pi OS with desktop, in the accessories menu there is an option to run a Text Editor. This is a simple editor which opens in a window like a normal awarding. It allows use of the mouse and keyboard, and has tabs and syntax highlighting.

You can use keyboard shortcuts, such as Ctrl + S to save a file and Ctrl + X to get out.

Thonny

Thonny is a Python REPL and IDE, so you can write and edit Python code in a window and run information technology straight from the editor. Thonny has independent windows, and syntax highlighting, and uses Python iii.

Geany

A fast and lightweight IDE, supporting many different file types, including C/C++ and Python. It is installed past default on Raspberry Pi Bone.

Text Editors in the Terminal

Nano

GNU Nano is at the like shooting fish in a barrel-to-use cease of command-line editors. It's installed by default, so use nano somefile.txt to edit a file, and keyboard shortcuts like Ctrl + O to save and Ctrl + X to exit.

Half dozen

Vi is a very old (c. 1976) control-line editor, which is available on nearly UNIX systems and is pre-installed on Raspberry Pi OS. Information technology's succeeded by Vim (Vi Improved), which requires installation.

Different most editors, Six and Vim accept a number of different modes. When you open 6 with vi somefile.txt, you start in command mode which doesn't directly permit text entry. Press i to switch to insert mode in order to edit the file, and type away. To save the file you must return to command mode, so press the Escape key and enter :w (followed by Enter), which is the command to write the file to disk.

To search for the give-and-take 'raspberry' in a file, brand sure yous're in command style (printing Escape), so type /raspberry followed by northward and N to flick forwards/backwards through the results.

To save and exit, enter the command :wq. To exit without saving, enter the command :q!.

Depending on your keyboard configuration, you may find your cursor keys don't work. In this case, yous tin can use the H-J-K-L keys (which move left, down, up, and correct respectively) to navigate the file in control mode.

Vim

Vim is an extension of Vi and works in much the same way, with a number of improvements. Just Vi is installed by default and so to get the full features of Vim, install it with APT:

You can edit a file in Vim with vim somefile.txt.

Emacs

Emacs is a GNU control-line text editor; it's powerful, extensible, and customisable. You lot can install it with APT:

You tin can use keyboard combination commands, such every bit Ctrl + Ten Ctrl + S to salve and Ctrl + X Ctrl + C to close.

Linux Users

User direction in Raspberry Pi Os is washed on the command line. The default user is pi, and the countersign is raspberry. You tin can add users and change each user's password.

Changing your Password

In one case yous're logged in as the pi user, it is highly advisable to utilize the passwd command to alter the default password to amend your Raspberry Pi's security.

Enter passwd on the command line and press Enter. You lot'll be prompted to enter your current password to authenticate, so asked for a new password. Press Enter on completion and y'all'll be asked to confirm it. Note that no characters will exist displayed while entering your password. Once you've correctly confirmed your password, you lot'll exist shown a success bulletin (passwd: countersign updated successfully), and the new password will apply immediately.

If your user has sudo permissions, you can change another user'due south password with passwd followed by the user'southward username. For example, sudo passwd bob will allow you to set the user bob's countersign, and then some additional optional values for the user such as their name. Just press Enter to skip each of these options.

Remove a User'due south Countersign

Yous can remove the password for the user bob with sudo passwd bob -d. Without a countersign the user will non exist able to login to a Terminal.

Note	This is useful for users that need to exist for system reasons, but y'all don't desire information technology to be possible to login to the account for security reasons.

Creating a New User

Yous can create additional users on your Raspberry Pi Bone installation with the adduser command.

Enter sudo adduser bob and you'll be prompted for a password for the new user bob. Leave this blank if you don't want a password.

Your Dwelling Folder

When you lot create a new user, they will have a home folder in /home/. The pi user'due south home folder is at /habitation/pi/.

The `skel` Command

Upon creating a new user, the contents of /etc/skel/ will be copied to the new user'due south dwelling binder. You lot tin can add together or modify dot-files such as the .bashrc in /etc/skel/ to your requirements, and this version will be applied to new users.

Deleting a User

You can delete a user on your system with the command userdel. Apply the -r flag to remove their home folder too:

Root and Sudo

The Linux operating system is a multi-user operating organization which allows multiple users to log in and utilize the computer. To protect the computer (and the privacy of other users), the users' abilities are restricted.

Most users are immune to run most programs, and to save and edit files stored in their own domicile folder. Normal users are not normally immune to edit files in other users' folders or any of the organisation files. In that location's a special user in Linux known as the superuser, which is normally given the username root. The superuser has unrestricted access to the computer and can do almost anything.

The `sudo` Command

Yous won't normally log into the computer equally root, but y'all can use the sudo command to provide access as the superuser. If y'all log into your Raspberry Pi as the pi user, then yous're logging in equally a normal user. Yous tin run commands as the root user by using the sudo control before the program you want to run.

For case, if yous want to install additional software on Raspberry Pi OS and then you normally use the apt tool. To update the list of available software, you demand to prefix the apt control with sudo:

sudo apt update

Y'all can also run a superuser shell past using sudo su. When running commands as a superuser there'south nothing to protect against mistakes that could damage the organisation. It'due south recommended that you only run commands equally the superuser when required, and to exit a superuser shell when it's no longer needed.

The Sudo'ers List

The default pi user on Raspberry Pi Bone is a member of the sudo group. This gives the ability to run commands as root when preceded by sudo, and to switch to the root user with sudo su.

To add a new user to the sudo group, use the adduser command:

Annotation that the user bob will be prompted to enter their password when they run sudo. This differs from the behaviour of the pi user, since pi is non prompted for their password. If you lot wish to remove the countersign prompt from the new user, create a custom sudoers file and place information technology in the /etc/sudoers.d directory.

Create the file using sudo visudo /etc/sudoers.d/010_bob-nopasswd.
Insert the following contents on a single line: bob ALL=(ALL) NOPASSWD: ALL
Relieve the file and exit.

In one case you have exited the editor, the file volition be checked for any syntax errors. If no errors were detected, the file will be saved and you volition be returned to the shell prompt. If errors were detected, yous will be asked 'what now?' Press the 'enter' key on your keyboard: this will bring upwardly a list of options. You volition probably want to apply 'eastward' for '(e)dit sudoers file again', so yous can edit the file and set the trouble.

Note	Choosing option 'Q' volition save the file with any syntax errors nevertheless in identify, which makes it impossible for any user to utilise the sudo command.

Note	Information technology is standard practice on Linux to have the user prompted for their password when they run `sudo`, since it makes the arrangement slightly more secure.

The `.bashrc ` File

In your home folder you will notice a subconscious file chosen .bashrc which contains some user configuration options. Yous can edit this file to suit your needs. Changes made in this file will be actioned the next time a last is opened, since that is when the .bashrc file is read.

If you desire your changes to have place in your current terminal, y'all can employ either source ~/.bashrc or exec bash. These really exercise slightly different things: the onetime simply re-executes the .bashrc file, which may result in undesirable changes to things similar the path, the latter replaces the electric current beat with a new bash shell, which resets the shell back to the state at login, throwing away any shell variables you lot may have prepare. Cull whichever is most appropriate.

Some useful adaptions are provided for you lot; some of these are commented out with a past default. To enable them, remove the and they will exist active next time y'all kick your Raspberry Pi or start a new final.

For example, some ls aliases:

alias ls='ls --color=machine' #alias dir='dir --color=auto' #alias vdir='vdir --color=motorcar'  allonym grep='grep --colour=auto' allonym fgrep='fgrep --color=auto' alias egrep='egrep --colour=auto'

Aliases similar these are provided to help users of other systems similar Microsoft Windows (dir is the ls of DOS/Windows). Others are to add together colour to the output of commands like ls and grep by default.

More variations of ls are also provided:

# some more than ls aliases #alias ll='ls -l' #allonym la='ls -A' #alias fifty='ls -CF'

Ubuntu users may be familiar with these every bit they are provided past default on that distribution. Uncomment these lines to have access to these aliases in futurity.

The `.bash_aliases` File

.bashrc also contains a reference to a .bash_aliases file, which does non exist past default. You lot can add it to provide a handy way of keeping all your aliases in a dissever file.

if [ -f ~/.bash_aliases ]; then     . ~/.bash_aliases fi

The if statement here checks the file exists before including information technology.

So you just create the file .bash_aliases and add more aliases similar and then:

You can add together other things directly to this file, or to another and include that file like the .bash_aliases example to a higher place.

Trounce Scripts

Commands can exist combined together in a file which can and then be executed. Equally an example, copy the post-obit into your favourite text editor:

                  #!/usr/bin/bash  while : do echo Raspberry Pi! done

Save this with the name fun-script.

Earlier you can run information technology you lot must first arrive executable; this can exist done by using the change manner command chmod. Each file and directory has its own set of permissions that dictate what a user can and can't exercise to it. In this case, by running the command chmod +x fun-script, the file fun-script volition now be executable.

Y'all can then run it by typing ./fun-script (assuming that it's in your current directory).

This script infinitely loops and prints Raspberry Pi!; to stop it, press Ctrl + C. This kills any command that'due south currently being run in the last.

Scheduling Tasks with Cron

Cron is a tool for configuring scheduled tasks on Unix systems. It is used to schedule commands or scripts to run periodically and at stock-still intervals. Tasks range from backing up the user's home folders every day at midnight, to logging CPU data every hour.

The command crontab (cron table) is used to edit the list of scheduled tasks in operation, and is done on a per-user ground; each user (including root) has their own crontab.

Editing the `crontab` File

Run crontab with the -east flag to edit the cron tabular array:

Note	The kickoff fourth dimension you run `crontab` you'll be prompted to select an editor; if you are not sure which one to employ, choose `nano` by pressing `Enter`.

Calculation a Scheduled Task

The layout for a cron entry is made upward of six components: minute, 60 minutes, twenty-four hour period of month, month of yr, day of week, and the command to be executed.

# m h  dom monday dow   command

# * * * * *  command to execute # ┬ ┬ ┬ ┬ ┬ # │ │ │ │ │ # │ │ │ │ │ # │ │ │ │ └───── day of calendar week (0 - 7) (0 to 6 are Sunday to Sabbatum, or use names; 7 is Sun, the same every bit 0) # │ │ │ └────────── month (one - 12) # │ │ └─────────────── day of month (one - 31) # │ └──────────────────── hour (0 - 23) # └───────────────────────── min (0 - 59)

For case:

0 0 * * *  /home/pi/backup.sh

This cron entry would run the backup.sh script every twenty-four hour period at midnight.

Viewing Scheduled Tasks

View your currently saved scheduled tasks with:

Erase scheduled tasks

Delete all currently scheduled tasks:

Running a Task on Reboot

To run a control every time the Raspberry Pi starts upwardly, write @reboot instead of the time and date. For case:

@reboot python /home/pi/myscript.py

This will run your Python script every time the Raspberry Pi reboots. If you want your command to exist run in the background while the Raspberry Pi continues starting up, add a space and & at the cease of the line, similar this:

@reboot python /home/pi/myscript.py &

The `systemd` Daemon

In order to have a command or programme run when the Raspberry Pi boots, you tin add together information technology as a service. In one case this is done, you can start/terminate enable/disable from the linux prompt.

Creating a Service

On your Raspberry Pi, create a .service file for your service, for example: myscript.service

[Unit of measurement] Description=My service After=network.target  [Service] ExecStart=/usr/bin/python3 -u main.py WorkingDirectory=/home/pi/myscript StandardOutput=inherit StandardError=inherit Restart=ever User=pi  [Install] WantedBy=multi-user.target

So in this case, the service would run Python 3 from our working directory /dwelling/pi/myscript which contains our python program to run principal.py. Only yous are not limited to Python programs: simply change the ExecStart line to be the control to starting time any program or script that you lot want running from booting.

Copy this file into /etc/systemd/system every bit root, for instance:

sudo cp myscript.service /etc/systemd/system/myscript.service

Once this has been copied, you accept to inform systemd that a new service has been added. This is washed with the following command:

sudo systemctl daemon-reload

Now y'all tin attempt to start the service using the following control:

sudo systemctl start myscript.service

Stop it using post-obit command:

sudo systemctl stop myscript.service

When you are happy that this starts and stops your app, y'all can have it showtime automatically on reboot by using this control:

sudo systemctl enable myscript.service

The systemctl command can also be used to restart the service or disable information technology from boot upwardly.

Note	The order in which things are started is based on their dependencies — this particular script should start fairly late in the boot process, after a network is available (see the After section). You tin configure unlike dependencies and orders based on your requirements.

Source: https://www.raspberrypi.com/documentation/computers/using_linux.html

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