Learn GNU/Linux Commands (7): Superuser - su, exit, sudo

-

When installing GNU/Linux, we are asked to set up the password for the superuser, or root. We are probably asked to set up a normal user as well. The superuser (root) has access to all files, including files that are intended for administrative use only. Normal users are not allowed to access these files. Some programs that alter these files need administration privileges, such as the package management tools that are used to install and remove other programs. We introduce the package management tools later.

We can grant normal users administration privileges with the program "sudo".

Switch user

su [USER]

Switch to USER, if USER is omitted, switch to root. "su" may stand for substitute.

To switch back, use "exit" or "su" with the username before.

exit

The two examples below do the same thing.

[Texpion@com ~]$ su
Password: 
[root@com ~]# su Texpion
[Texpion@com ~]$ 
[Texpion@com ~]$ su root
Password: 
[root@com ~]# exit
[Texpion@com ~]$

Normally "exit" will exit (close) the shell.

sudo

Sudo, sometimes considered as short for Superuser do. If a normal user becomes a sudoer, this user can run various commands as root without needing the root password by adding "sudo " in front of the commands. For example, to edit a configuration file that is intended to by modified by administrators only, with "vi": 

[Texpion@com ~]$ sudo vi config_file

The program "sudo" may not be installed be default in distros such as Debian. Though it can be installed manually.

We can set a user as an administrator (sudoer) when we are installing the system if this option is available. We can also edit the configuration file "/etc/sudoers" only with the command "visudo". To make changes, after open the editor, follow the comments. It is not recommended for beginners to edit this file.

We can also add a normal user in the sudoer's group. We introduce group in the next part.

Related

Comments

Post a Comment

Popular

Intel 7th and 8th generation processor graphics driver for Windows 7/8/8.1

-
For Intel's 7th and 8th generation processors, the only Windows operating system that Intel supports is Windows 10 x64. There is no official driver for Windows 7, Windows 8, or Windows 8.1. But according to this YouTube video https://www.youtube.com/watch?v=7w9JofZQkxI , the Windows 7's Driver for the 6th gen processors can be installed for the 7th gen processors. According to 6th Generation Intel® Processor for U/Y-Platforms Datasheet, Volume 1 of 2 , 7th Generation Intel® Processor Families for S Platforms Datasheet, Volume 1 of 2 , 7th Generation Intel® Processor Families for U/Y Platforms and 8th Generation Intel® Processor Family for U Quad Core Platforms Datasheet, Volume 1 of 2 , 8th Generation Intel® Processor Family for S-Processor Platforms Datasheet, Volume 1 of 2 , The graphics processors on not only Intel 6th gen mobile, but also all 7th and 8th gen processors are all based on Gen 9 LP (generation 9 Low Power) graphics core architecture. The graphics driv
Read more

AV1 vs VP9 vs AVC (h.264) vs HEVC (h.265): Part II - Fidelity

-
Image
In this part, we tested the lossy compression capability. "Lossy" means that in order to reduce data size, the data is inexactly approximated and part of it is discarded. To measure the fidelity of the reconstruction (encoded video) of lossy compression codecs in our tests, we used PSNR (Peak signal-to-noise ratio). The greater the PSNR of two videos, the more similar they are. If the encoded video is lossless, the PSNR will be infinity when compared to the original. We tried to match the PSNR and compared the video stream size, the smaller the size, the better the codec. But it is hard to make the PSNR exactly the same. As mentioned earlier, as of June 2018, the AV1 is still experimental and we were not able to set its constant quality mode as we expected. And AV1 is extremely slow. So we did the AV1 in its vibrate bitrate mode first. We have found that the VP9 produces better results when encoded in its 2-pass constant quality mode (can be set with "-crf"), so
Read more

AV1 vs VP9 vs AVC (h.264) vs HEVC (h.265): Part I - Lossless

-
Image
Conclusion In terms of lossless compression, x264 and x265 took less time and produced smaller files. All video codecs produced smaller video files than LZMA/LZMA2, the general purpose compression algorithms. In our tests, AV1 takes approximately 160-190x more time than x264 to encode in their lossless mode. AV1 does have a lossless mode, but the output is not lossless at all. VP9 and AV1 can take advantage of multi-threading, but they can not load all CPU cores all the time as x264 and x265 do. Note At of June 2018, AV1 is still experimental. We used x264 as the AVC encoder. We used x265 as the HEVC encoder. We used pxz as the LZMA/LZMA2 compressor. LZMA is also the default algorithm of 7-Zip. The AV1 encoder ran with "--cpu-used=4" for "medium" speed, "--tile-columns=4" to enabling multi-threading. All encoders ran in their lossless mode, all other settings were as default. Test 1 Source video sintel_trailer_2k_480p24.y4m © copyright
Read more

OBS Studio settings for best quality (loseless) recording

-
Image
OBS - Open Broadcaster Software. Change Color Format to RGB. Recorded videos can be played in VLC and other FFmpeg-based players. Choose FFmpeg and select matroska as the container, libx264rgb as the video encoder, flac as the audio encoder. If your video editor does not support RGB format, select other color format and select libx264 as the video encoder. Decrease the keyframe interval if you have trouble playing the recorded video. For 1080p60fps videos, because the bitrate is so high, even though you set the keyframe interval to 60 (default is 250), you may still have trouble playing the video sometimes, That doesn't mean that the video is broken. If you don't care about playing the recorded video or you transcode it later anyway, you can set the keyframe interval to 600. Video Encoder Settings: preset=ultrafast x264-params=qp=0 :psy=0:fast_pskip=0:ipratio=1.0:pbratio=1.0 To record 1080p60fps videos, it required at least 3 Intel Core i5 cores at 4.5GHz and the bitrat
Read more

AV1 vs VP9 vs AVC (h.264) vs HEVC (h.265): Part III - Quality

-
Image
Visual quality is somewhat subjective. However, Efforts are still being made to quantify it. There is a perceptual video quality assessment algorithm developed by Netflix called VMAF - Video Multi-Method Assessment Fusion. We tried to tune different CRF values to encode the video clips we used in previous parts. But unfortunately, we found that decreasing the CRF did not increase the VMAF score, it even dropped a little bit. We are not able to do a quality comparison at this moment. Anyway, a feature of x264 called Psy RDO caught our attention: the human eye doesn't just want the image to look similar to the original, it wants the image to have similar complexity. Therefore, we would rather see a somewhat distorted but still detailed block than a non-distorted but completely blurred block. The result is a bias towards a detailed and/or grainy output image, a bit like xvid except that its actual detail rather than ugly blocking. This preference is quite easy to understand, peopl
Read more

AV1 vs VP9 vs AVC (h.264) vs HEVC (h.265): Part IV - Decode

-
Image
In this part, we tested the decoding speed. Especially for video coding formats designed for video transmissions over the Internet, decoding speed could be much more important than encoding speed. We tried to encode in 2-pass vibrate bitrate mode (VBR) to get almost the same file sizes and counted the time needed for converting the encoded videos into raw video files. we decoded in RAM, because decoding is fast and the raw video could be very large. We also encoded in RAM this time, but the improvement of encoding speed, if any, wasn't very impressive. Conclusion At of June 2018, the AV1 decoder can only decode in a single thread. Decoders for H.264, H265, and VP9 utilize multi-threads. We were not able to play videos encoded with AV1 in Chrome, Firefox Nightly, VLC, both on Windows and LINUX, though those are claimed to be able to. To decode the files encoded with AV1, the CPU time was approximately 3.5-6x longer than that to decode files encoded with x264. This means that i
Read more

Install VMAF on Fedora, CentOS/Red Hat (RHEL)

-
VMAF - Video Multi-Method Assessment Fusion. Tested on Fedora 28. For CentOS/Red Hat (RHEL), replace dnf with yum . The following commands install dependencies, download source files from github.com and compile VMAF. sudo dnf install gcc gcc-c++ gcc-gfortran freetype hdf5 git \ python2-tkinter python-numpy python-scipy python-matplotlib python-notebook python-pandas python-sympy python-nose python-scikit-learn python-scikit-image python-h5py git clone https://github.com/Netflix/vmaf.git cd vmaf git submodule update --init --recursive make echo export PYTHONPATH="$(pwd)/python/src:$(pwd)/sureal/python/src:$PYTHONPATH" >> ~/.bashrc source ~/.bashrc sudo make install # Optional Install On Other Distros For more info, or if you want to install it on Ubuntu or other distros, visit https://github.com/Netflix/vmaf/blob/df1d890eb6a6d0465d8e1b2a35d81fc60a1bd53a/README.md . Related AV1 vs VP9 vs AVC (h.264) vs HEVC (h.265): Part I - Lossless AV1 vs VP9 vs AVC (h.264) v
Read more