Linux FAQs - andreimironenko/oe-davinci GitHub Wiki
Use this command
$ top
You should see the output similar to that:
File:Linux-cpu-utilization.png
This is an excerpt from Linux write man:
...
"This function is a cancellation point in multi-threaded programs. This is a problem if the thread allocates some resources (like memory, file descriptors, semaphores or whatever) at the time write is called. If the thread gets canceled these resources stay allocated until the program ends. To avoid this, calls to write should be protected using cancellation handlers."
...
Literally, it says that if you kill (by calling pthread_kill) or exit from the main while the write operation is in progress in other threads, it can be a problem! We've observed this behaviour while playing sound on HTC. Sometimes I2C bus gets stuck. Although this is partly a driver problem, the application should always exits gracefully.
The easiest way for this, when for instance your program received SIGINT(Ctrl+C), introducing a stop_flag which can be seen and checked by all threads. I have a simple test app, which performs stress test for I2C bus. There some threads which perform read/write to the certain I2C devices like EEPROM, audio, RTC. You can get it from here:
git clone git@amuxi:/opt/git/htc/tests/i2c.git
password - git
In practice read/write to this flag should be atomic operations, but as in this implementation I only change this flag from signal handler, I skipped it for simplicity.
Simple run dmesg command
$ dmesg | grep tty
Output:
[ 37.531286] serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A [ 37.531841] 00:0b: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A [ 37.532138] 0000:04:00.3: ttyS1 at I/O 0x1020 (irq = 18) is a 16550A
Another way - use of setserial command
setserial is a program designed to set and/or report the configuration information associated with a serial port. This information includes what I/O port and IRQ a particular serial port is using, and whether or not the break key should be interpreted as the Secure Attention Key, and so on. Just type the following command:
$ setserial -g /dev/ttyS[0123]
Output:
/dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4 /dev/ttyS1, UART: 16550A, Port: 0x1020, IRQ: 18 /dev/ttyS2, UART: unknown, Port: 0x03e8, IRQ: 4 /dev/ttyS3, UART: unknown, Port: 0x02e8, IRQ: 3 setserial with -g option help to find out what physical serial ports your Linux box has.
Have ready .iso file and plug-in pen-drive. By issuing this command
dmesg | tail -20
find the device node assigned to the pen-drive. Usually it should be like /dev/sdg1 (or /dev/sdb).
Unmount all the partions of the pen-drive
sudo umount /dev/sdg
Write ISO image to the destination drive
dd if=~/ubuntu.iso of=/dev/sdg
wait until it completes and make sync with cache to avoid any possible loss
sync
It's ready now just remove pen-drive.
To check all drives use this command
$ df -h
To check the concrete directory structure use
$ du -ahc
Look at this article for more "du" command examples.
First use of free command
root@dm365-htc:~# free
total used free shared buffers
Mem: 125672 21956 103716 0 1180
Swap: 0 0 0
Total: 125672 21956 103716
Or use of top
root@dm365-htc:~# top
the output should be like this:
File:Linux-ram-size-top-command-usage.png
It's very useful article. I used this VIM command:
: %s/^\(.*\)\(\n\1\)\+$/\1/
Install nmap util
$ sudo apt-get install nmap
then run this command
$ sudo nmap -sP 10.42.43.*
you should get the output like this:
Starting Nmap 5.21 ( http://nmap.org ) at 2012-06-26 14:32 BST Nmap scan report for 10.42.43.1 Host is up. Nmap scan report for htc (10.42.43.2) Host is up (0.00081s latency). MAC Address: 36:4B:97:7A:2C:5A (Unknown) Nmap scan report for 10.42.43.26 Host is up (0.0016s latency). MAC Address: 00:14:2D:48:71:32 (Toradex AG) Nmap done: 256 IP addresses (3 hosts up) scanned in 2.17 seconds
Use this line
dmesg | tail -n 50
it prints last 50 lines of the kernel log
Run
alsamixer
And find what widgets(input/output lines) are available
In our case, there is "Digital" output so run this command to mute
amixer set Digital 0%
to restore the desired level run the same command
amixer set Digital 93%
What scp shouldn't be used for:
- When you are copying more than a few files, as scp spawns a new process for each file and can be quite slow and resource intensive when copying a large number of files.
- When using the -r switch, scp does not know about symbolic links and will blindly follow them, even if it has already made a copy of the file. The can lead to scp copying an infinite amount of data and can easily fill up your hard disk, so be careful.
rsync has very similar syntax to scp:
rsync -e ssh [-avz] /some/file [ more ... ] host.name:/destination/file
-or-
rsync -ave ssh user@server:/path/to/source /destination/dir
rsync's speciality lies in its ability to analyse files and only copy the changes made to files rather than all files. This can lead to enormous improvements when copying a directory tree a second time.
Switches:
-a Archive mode, most likely you should always keep this on. Preserves file permissions and does not follow symlinks.
-v Verbose, lists files being copied
-z Enable compression, this will compress each file as it gets sent over the pipe. This can greatly decrease time depending on what sort files you are copying.
-e ssh Uses ssh as the transport, this should always be specified.
Disadvantages of using rsync:
- Picky syntax, use of trailing slashes can be confusing.
- Have to remember that you are using ssh.
- rsync is not installed on all computers.
Look at this article about how to set NAT up in linux.
Look at this very useful article from TI.
When you plug-in your card system assigns device ID for the card. You need this information for passing it to dd command. To define your card device ID run this command
$ dmesg | tail -n 20
which will print last 20 lines of kernel log messages, so it should look like this
[1552603.677544] sd 39:0:0:0: Attached scsi generic sg7 type 0 [1552603.680738] sd 39:0:0:0: [sdg] Attached SCSI removable disk [1552820.685519] usb 1-4: USB disconnect, address 62 [1557138.262634] sd 37:0:0:2: [sdd] 3926016 512-byte logical blocks: (2.01 GB/1.87 GiB) [1557138.263727] sd 37:0:0:2: [sdd] Assuming drive cache: write through [1557138.265621] sd 37:0:0:2: [sdd] Assuming drive cache: write through [1557138.266686] sdd: sdd1 [1557139.099516] EXT2-fs (sdd1): warning: mounting unchecked fs, running e2fsck is recommended
From this print, it easy to define that my card is /dev/sdd.
Now we are ready. Have your image on place, in my case this is sdk1.2.x.img and issue dd command to write to SD card
$ sudo dd if=sdk1.2x.img of=/dev/sdd
Be patient for sometime, depending on the image size it can take up to 5-10 minutes.
Don't remove your card while dd command is in the progress! It might destroy the card!
Once it finishes your card is ready to use :-)
$ du -k | sort -n | tail -40
Serial port loopback duplex test
Or I used these simple method
On a target run this command, which will generate infinite stream of random bytes to serial:
$ cat /dev/urandom > /dev/ttyUSB0
on the desktop just run minicom. You might need to alter the serial port settings, try to play with settings util you get a flow of random bytes.
Look at this article.
For the application side, syslog is the answer, use this link for further information.
For the kernel side (printk) messages use dmesg command to retrieve the latest log.
The command "time" with followed command under investigation will give the execution time:
$ time cp xdctools_setuplinux_3_16_03_36.bin xdctools_setuplinux.bin
real 0m21.773s user 0m0.008s sys 0m0.268s
I ran "copy" while OE build was in progress so it slowed down write operation and as you see copy the image took 21.773 s.
To disable
$ sudo ufw disable
to enable back
$ sudo ufw enable
I found this article quite useful. I also copy context of it here.
In quite a few situations its preferred to have ssh keys dedicated for a service or a specific role. Eg. a key to use for home / fun stuff and another one to use for Work things, and another one for Version Control access etc. Creating the keys is simple, just use
ssh-keygen -t rsa -f ~/.ssh/id_rsa.work -C "Key for Word stuff"
Use different file names for each key. Lets assume that there are 2 keys, ~/.ssh/id_rsa.work and ~/.ssh/id_rsa.misc . The simple way of making sure each of the keys works all the time is to now create config file for ssh:
touch ~/.ssh/config chmod 600 ~/.ssh/config echo "IdentityFile ~/.ssh/id_rsa.work" >> ~/.ssh/config echo "IdentityFile ~/.ssh/id_rsa.misc" >> ~/.ssh/config
This would make sure that both the keys are always used whenever ssh makes a connection. However, ssh config lets you get down to a much finer level of control on keys and other per-connection setups. And I recommend, if you are able to, to use a key selection based on the Hostname. My ~/.ssh/config looks like this :
Host *.home.lan IdentityFile ~/.ssh/id_dsa.home User kbsingh
Host *.vpn IdentityFile ~/.ssh/id_rsa.work User karanbir Port 44787
Host *.d0.karan.org IdentityFile ~/.ssh/id_rsa.d0 User admin Port 21871
Ofcourse, if I am connecting to a remote host that does not match any of these selections, ssh will default back to checking for and using the 'usual' key, ~/.ssh/id_dsa or ~/.ssh/id_rsa.
You can get Hanover public and private keys here:
hanover-system-dev/recipes/hanover-security/hanover-security-git
Unfortunately it must be done on a target
dropbearconvert openssh dropbear ./hanover.id_rsa hanover.id_rsa.db
Afterwards this private key can be used for password-less SSH access to other devices
ssh -i ./hanover.id_rsa.db [email protected] ls
Make sure to install cifs-utils package:
sudo apt-get install cifs-utils
create a mount point under /media
sudo mkdir -p /media/development
then mount the share by issuing this command
sudo mount.cifs //192.168.0.10/development /media/development -o user=yourusername pass=yourpassword dom=HANOVER.LOCAL
Start browsing /media/development!
Copy filet to FTP server
curl --anyauth -T ./ready_IP_TFT ftp://[email protected]/obc-iv/
Get list of files from FTP server
for (( f=0 ; f < ${#list_files[*]} ; f++ )) ; do
echo ${list_files[$f]}
done
Download a single file
curl -O ftp://[email protected]/obc-iv/ipk/IP_TFT/amironenko/iptft.r01-rc03.tar.bz2
Delete a single file obc-iv/ready_IP_TFT from server ftp://[email protected]/, using anonymous FTP user which denoted ftp@
curl --quote "DELE obc-iv/ready_IP_TFT" ftp://[email protected]/
While modifying or creating a custom BSP for the embedded Linux, one of the many things which needs better understanding is Inittab. Inittab describes which processes are started during bootup. It is the job of init to read the inittab file and start the necessary application.
Format of each entry in the inittab resembles:
< id >:< runlevels >:< action >:< process >
Where < id >: The id field is used by BusyBox init to specify the controlling tty for the specified process. If BusyBox detects that a serial console is in use, then the id field is ignored.
< runlevels >: The runlevels field is ignored buy busybox. Init used in desktop systems also understands runlevels. However, init which comes with busybox doesn't support runlevels. If runlevels are needed sysvinit should be used in place init.
< action >: Valid actions include sysinit, respawn, askfirst, wait, once, restart, ctrlaltdel, and shutdown.
- sysinit :The process will be executed during system boot. It will be executed before any boot or bootwait entries.
- respawn :The process will be restarted whenever it terminates
- askfirst : The askfirst actions acts just like respawn, except that before running the specified process it displays the line "Please press Enter to activate this console." and then waits for the user to press enter before starting the specified process.
- ctrlaltdel :The process will be executed when init receives the SIGINT signal. This means that someone on the system console has pressed the CTRL-ALT-DEL key combination. Typically one wants to execute some sort of shutdown either to get into single-user level or to reboot the machine.
Few examples from busysybox inittab:
::sysinit:/etc/init.d/rcS
Put a getty on the serial line (for a terminal)
::respawn:/sbin/getty -L ttyS 115200 vt100
# Stuff to do when restarting the init process ::restart:/sbin/init
# Stuff to do before rebooting ::ctrlaltdel:/sbin/reboot
At first list all available I/O areas
$ cat /proc/iomem
You should see something like this
48030100-480301ff : omap2_mcspi.1 48030100-480301ff : omap2_mcspi.1 48032000-48032fff : omap_gpio.0 4804c000-4804cfff : omap_gpio.1
Please notice, these are PHYSICAL addresses not VA. To list first 10 16-bit words in gpio.0, beginning at address 0x48032000
$ dd if=/dev/mem skip=$((0x481ac000)) bs=$((0x10)) count=10 2> /dev/null | hexdump -C
00000000 37 ff ff bb ff ff fa db bf ff fe ef f7 ff ff b7 |7...............| 00000010 2f df f7 c9 7f ff ff bf 67 ff ff fe ff cf ff fe |/.......g.......| 00000020 ff eb ff fe ff ff ff f7 ff df ff ff ff 9a ff ff |................| 00000030 7f bb ef ff ff ff f7 7f ff df bf bf ff ef ff fb |................| 00000040 eb 7f 97 f7 f3 ff ef eb f7 ff ff f9 fa bf fe af |................| 00000050 ff dd ff ff df f5 ff df ff ed be fd df bf fe dc |................| 00000060 df ff f6 f7 df ff ff bf f7 ff be f7 ff d6 ef bf |................| 00000070 ff f3 ff 7f bb ff ff fc db ff ff ff ef ff f7 fe |................| 00000080 b7 73 df fb ff ff ff ff fb db ef ff ff be b7 7f |.s..............| 00000090 f8 df ff fe ff df ff ff df 76 7f fe bf fd 9f fc |.........v......|
Write data
dd if=datafile of=/dev/kmem bs=1 seek=805e000 conv=notrunc
find . -regex ".*\.\(c\|sh\|inc\|cpp\|h\|hpp\)" -exec grep -Hn "\/dev\/null" {} \; -print | tee -a ~/dev.null.log
There are two parts in this command: find and grep. Find searches for all files with the extensions given in regex and grep search for the text pattern "/dev/null" in them.
One possibility I found for redirecting logs to the remote machine:
ls -R | ssh [email protected] "cat > /dev/tty1"
Similarly to the other terminal on the same machine:
ls -R | cat > /dev/tty1
to store output to the local file as well do
for the remote tty:
ls -R | tee -a cmd.log | ssh [email protected] "cat > /dev/tty1"
for other local tty:
ls -R | tee -a cmd.log | cat > /dev/tty1