Operating Systems

OSX

• I don’t know what caused it, but I am getting this error everytime I restart the computer
  • Core Telephony Trace File Error A file operation for CoreTelephony tracing has failed, you may be out of disk space. Details 'Error opening file /tmp/ct.shutdown, err = Operation not permitted
  • I solved this bug using the following technique:
    • Boot mac in recovery mode. Start / restart the machine When you hear login sound press and hold the Cmd + R keys (simultaneously) Release the keys when you see the recovery screen (Not the usual apple logo !!) Login might take slightly more longer than usual.
    • Select Utilities -> terminal and execute the following command csrutil disable Then restart the machine. The error was gone. Again go to recovery mode and execute csrutil enable Again restart the machine.
• I also faced the following error while installing torch dependencies
  • hdiutil: mount failed - no mountable file systems I fixed the bug using the same procedure as above.
  • To boot mac in safe mode. Start / restart the machine When you hear login sound press and hold the shift key Release the shift key when you see the apple logo Login might take slightly more longer than usual.
• When, I tried to run bin/nutch readseg, I got the error “Error: JAVA_HOME is not set”. However, it was set in ~/.bashrc. Then I executed the following command and things looked fine from then onwards. export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_122.jdk/Contents/Home
• When you ssh from your mac to a linux machine, you might see the following error/warning: Cannot set LC_CTYPE to default locale: No such file or directory. To fix it, goto iTerm –> Profiles –> Open Profiles –> Default Profile –> Edit Profiles –> Terminal –> Uncheck set environment variables automatically.

Ubuntu

• If you get the following error while running sudo apt-get update
  • W: GPG error: http://ppa.launchpad.net trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 82EB5823F4FE239D
  • Then, set $http_proxy and execute the following command.
  • sudo apt-key adv --keyserver-options http-proxy=$http_proxy * --keyserver keyserver.ubuntu.com --recv 82EB5823F4FE239D
• Fresh install of Ubuntu 18.04.1: Was facing a lot of trouble connecting to internet. “WiFi adapter not found”
  • As per my understandin, the problem was WiFi drivers were missing.
  • Went to BIOS and confirmed that my WiFi device is AP6212/6255
  • Upon searching the web, I’ve understood that it has something to do with bcm 43455
  • I followed the solution in this link https://askubuntu.com/questions/1003350/bcm43455-pcie-wireless-adapter-not-recognised
  • Another popular solution was sudo apt install –reinstall bcmwl-kernel-source (It did not work in my case)

General

• You can upload data to google drive using ssh by using gdrive following
  • the process mentioned here.
• If you ssh into a server and then do sudo -u some-user-name -i then * you cannot use “screen command”.
  • To use the screen command issue the following command while you are logged * in as some-user-name script /dev/null
  • The user who executes this command, basically owns the shell.
• To add a user in the linux environment and to give him sudo access cat /etc/passwd gives the set of all users in the given machine sudo adduser user_name - Fill in the required details sudo adduser user_name sudo - Gives sudo permission to the user
• To increase the priority of a process use the following command: renice -n nice_value -p process_id A nice_value of -20 means highest priority, default is 0
• While deleting or removing a large number of files. You might face the error: gnubin/rm: Argument list too long. In that case, use the xargs find . -maxdepth 2 -name "\*.txt" -print0 | xargs -0 rm
• Command to delete empty files from a directory find . -empty -type f * -delete
• cp, scp or sftp error: "File too large". It might be a limit problem, which can be set from the command line. check file transfer limit: ulimit -a Or check if your disk [to which you are copying is formatted in FAT32 or ext3]. ext4 is good.
• To perform a multi-threaded download on a Linux based machine - use “axel” command. axel -n 1000 url. Where 1000 is the number of threads.
• To use terminal as a browser [Extremely helpful for remote logins] sudo apt-get install w3m w3m-img
  • To open a webpage simply type in a terminal window: w3m URL-of-the-webpage To go back one page: Shift-B To open a new tab: Shift-T
  • To click a link: Navigate to the relevant portion using cursor / mouse and press Enter
  • To enter credentials like username and password, navigate to relevant portion and press Enter
  • Press Q to quit More help is available here w3m can also be run using screen: screen -L w3m URL-of-the-webpage

ldconfig

• ldconfig is a program that is used to maintain the shared library cache. This cache is typically stored in the file /etc/ld.so.cache and is used by the system to map a shared library name to the location of the corresponding shared library file.
• This is used when a program is executed to find locations of shared libraries that need to be dynamically loaded and linked to the program.
• By default, the shared library files in /lib, /usr/lib and a few other standard directories are maintained in the cache by ldconfig A new program or library might be installed in a non-standard directory, for example in /opt/foobar/lib. Programs that need the shared libraries from this library might fail with this error when executed. To fix this problem, we need to add the library directory to the list used by ldconfig. There are two ways to do this:
  • Add to LD_LIBRARY_PATH (Example export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/opt/foobar/lib in ~/.bashrc)
  • Rebuild cache by executing wither of the following commands ldconfig or ldconfig -v (verbose).
  • To check if the shared library cache now includes the shared libraries from the new directory use ldconfig -p A detailed description is here

Installing Apache2 on ubuntu

• Most basic usage: You can setup a simple file server which can serve files to users accessing your IP. Installation sudo apt-get install apache2 Scenario 1: You want to setup multiple virtual hosts on the same machine.

  • Edit the /etc/hosts file and include the hosts in the following manner

    127.0.0.1 localhost 127.0.0.1 myhost1 127.0.0.1 myhost2
    

  • Although, there are other places where you can add configurations. I have made all configuration changes in the following file - /etc/apache2/sites-enabled/000-default.conf:

    <VirtualHost *:80> ServerName myhost1 ServerAdmin my@emailid.com
    # The place where the index.html exists
    DocumentRoot /home/i1392424/Tools/brat-v1.3_Crunchy_Frog
    
    # Directory specific permissions
    <Directory /home/i1392424/Tools/brat-v1.3_Crunchy_Frog>
      AllowOverride Options Indexes FileInfo Limit AddType
      application/xhtml+xml .xhtml AddType font/ttf .ttf
    </Directory>
    
    ErrorLog ${APACHE_LOG_DIR}/error.log CustomLog
    ${APACHE_LOG_DIR}/access.log combined
    </VirtualHost>
    
    <VirtualHost *:80>
    # The server name should be defined in /etc/hosts
    ServerName myhost2 ServerAdmin my@emailid.com
    # The place where the index.html exists
    DocumentRoot /this/is/another/folder
    # Directory specific permissions
    <Directory /this/is/another/directory> AllowOverride Options Indexes
      FileInfo Limit AddType application/xhtml+xml .xhtml AddType font/ttf
      .ttf </Directory> ErrorLog ${APACHE_LOG_DIR}/error.log CustomLog
    ${APACHE_LOG_DIR}/access.log combined </VirtualHost>
    

  • After you change configuration execute the command sudo service apache2 restart or apache2 restart

  • You can now access your stuff from your browser http://myhost1 or http://myhost2

  • Disadvantage: The main disadvantage of this approach is that, while you can have multiple virtual hosts configured for multiple projects - Other people (within the same network) cannot access all these applications. They can only access the application hosted on the default port 80. For this reason, we might prefer hosting one application per host, which brings us to Scenario 2.

• Scenario 2: You want to setup multiple applications on the localhost itself. Add the following to /etc/apache2/sites-available/000-default.conf:

  <VirtualHost *:9001>
  # The server name should be defined in /etc/hosts
  ServerName localhost ServerAdmin my@emailid.com
  # The place where the index.html exists
  DocumentRoot /home/i1392424/Tools/brat-v1.3_Crunchy_Frog
  # Directory specific permissions
  <Directory /home/i1392424/Tools/brat-v1.3_Crunchy_Frog> AllowOverride
  Options Indexes FileInfo Limit AddType application/xhtml+xml .xhtml
  AddType font/ttf .ttf </Directory> ErrorLog ${APACHE_LOG_DIR}/error.log
  CustomLog ${APACHE_LOG_DIR}/access.log combined
  </VirtualHost>
  
  
  <VirtualHost \*:9002>
  # The server name should be defined in /etc/hosts
  ServerName localhost ServerAdmin my@emailid.com
  # The place where the index.html exists
  DocumentRoot /this/is/another/folder
  # Directory specific permissions
  <Directory /this/is/another/directory> AllowOverride Options Indexes
  FileInfo Limit AddType application/xhtml+xml .xhtml AddType font/ttf
  .ttf </Directory> ErrorLog ${APACHE_LOG_DIR}/error.log CustomLog
  ${APACHE_LOG_DIR}/access.log combined </VirtualHost>
  # Opening the ports for listening, very improtant
  Listen 9001
  Listen 9002
  

  • After modifying the conf file, execute one of the following commands sudo service apache2 restart or apache2 restart. Now others can connect to the respective applications from their browsers using http://your-local-ip:9001 and http://your-local-ip:9002
  • General notes
    • Do not have Listen <Port-ID> command in 2 places - ports.conf, sites-available/something.conf You can also create multiple files under sites-available like sites-available/something.conf. In that case you need to activate the site using the command sudo a2ensite something.conf
  • uTorrent (read mu-torrent) is a good software to download large files from torrent. If you are using command line, then use deluge
    • sudo apt-get install deluge deluged deluge-console
    • Run deluged
    • Run deluge-console

FTP Server related instructions

• You can use a tool called FileZilla as a ftp client. It is useful for downloading as well as uploading files into an ftp server. To transfer directories to an FTP server from a command line, follow the below outlined instructions.
• Install lftp in ubuntu
  • lftp <server-ip>
  • user <nikhil.pattisapu>
  • set ssl:verify-certificate no
  • mirror -R <path-to-local-dir> <path-to-server-dir>
• To transfer individual file to an FTP server from a command line, follow the instructions outlined below.
  • lftp <server-ip>
  • user <nikhil.pattisapu>
  • set ssl:verify-certificate no
  • ls
  • cd <server-target-directory>
  • put <host-source-directory>