Getting Hostname in Bash in Linux

Posted on

In Bash, how to get the hostname of the node running the program? In Bash, you can get the hostname of the node in at least 2 ways: Use the variable $HOSTNAME. Get the hostname by command hostname. Get the content of /proc/sys/kernel/hostname Example: $ echo $HOSTNAME host01 $ hs=`hostname` $ echo $hs host01 $
Read more

How to put files with spaces in names into HDFS?

Posted on

I got this error when I tried to save a file with a space in its name into HDFS: $ hdfs dfs -put -f “/home/u1/testa/test a” “/u1/testa/test a” put: unexpected URISyntaxException while the HDFS seems allow spaces in its file names: https://hadoop.apache.org/docs/r2.7.3/hadoop-project-dist/hadoop-common/filesystem/model.html . How to achieve the effect of saving the files with spaces in
Read more

Why I got message “invalid syntax, continuing…” when I execute “sysctl”?

Posted on

When I tried to apply new configuration in /etc/sysctl.conf, I got following message. warning: /etc/sysctl.conf(44): invalid syntax, continuing… Sounds like your changed /etc/sysctl.conf has problem. You may post the content of your /etc/sysctl.conf here to let other have a check. net.ipv4.ip_forward = 0 net.ipv4.conf.default.rp_filter = 1 net.ipv4.conf.default.accept_source_route = 0 kernel.sysrq = 0 kernel.core_uses_pid = 1
Read more

How to use the xargs argument twice in the command on Linux?

Posted on

`xargs` passes the argument once to the utility command specified. For example, xargs cat will cat every line passed to xargs. But how to use the xargs argument twice in the command on Linux? For example, to rename file to file.bak where file is from the stdin. One solution is to write a small script like
Read more

How to manually kill HDFS DataNodes?

Posted on

stop-dfs.sh report that there are no datanodes running on some nodes like hdfs-node-000208: no datanode to stop However, there are DataNode process running there. How to clean these processes on many (100s) of nodes? You may use this piece of bash script: for i in `cat hadoop/etc/hadoop/slaves`; do echo $i; ssh $i ‘jps | grep
Read more

How to Passwordless SSH to an OpenWrt Router?

Posted on

The good ssh-copy-id method which works well on common Linux seems not working for OpenWrt router. How to Passwordless SSH to an OpenWrt Router? OpenWrt’s SSH server is Dropbear. It can accept normal RSA keys. But the authorized_keys location is not the same as the openssh “~/.ssh/authorized_keys”. The location for the authorized_keys is /etc/dropbear/authorized_keys What
Read more

Printing “powernow-k8 transition frequency failed” after install XEN

Posted on

After I installed XEN hypervisor, the tty0 (CTRL+ALT+F1) prints “powernow-k8 transition frequency failed” to STDOUT continously, how to solve it? sudo rmmod powernow_k8 From https://lists.debian.org/debian-user/2013/01/msg00754.html How to make the settings persistent (take effect after reboot)? 1, Create script file ‘/etc/init.d/stop_pwoerk8.sh’ as follows. harry2vera@node1:/etc/init.d$ cat stop_pwoerk8.sh #! /bin/sh rmmod powernow_k8 2, Add the full PATH of
Read more

How to exclude last N columns in Bash on Linux?

Posted on

How to exclude last N columns of a string in bash? The point is that the number of columns in each line is uncertain (but > N). For example, I would like to remove the last 2 columns separated by ‘.’ in the following lines. systemd.3.gz systemd.mount.3.gz systemd.mount.f.3.gz The simple cut command cut -d’.’ -f1
Read more

How to check the DNS I am using on Linux?

Posted on

My Linux distro is Linux Mint 17 (Ubuntu 14.04.1 LTS (Trusty Tahr)). I am using NetworkManager. The old trick does not work: $ cat /etc/resolv.conf # Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8) # DO NOT EDIT THIS FILE BY HAND — YOUR CHANGES WILL BE OVERWRITTEN nameserver 127.0.1.1 If you are using
Read more

How to find the history of updated packages by apt-get or aptitude?

Posted on

How to find the history of updated packages by apt-get or aptitude? The history is in log files of dpkg and apt: /var/log/dpkg.log /var/log/apt/history.log /var/log/aptitude To check the recently installed packages: cat /var/log/dpkg.log | grep ” install ” To list history of recently installed packages by apt-get: cat /var/log/apt/history.log | grep ” install ” To
Read more

Filter away non-printable ASCII characters on Linux?

Posted on

Sometimes the commands’ output have some non-printable ASCII characters. How to filter away these non-printable ASCII characters on Linux? You can consider the problem as “how to leave only printable ascii characters?”. The printable characters in ASCII table are: Octal 011: Tab Octal 012: Line Feed Octal 015: Carriage Return Octal 040 to 176: printable
Read more

How to exclude users from GDM login screen?

Posted on

How to exclude users from appearing in the GDM login screen of Gnome 3? There is a long-time bug related to this ( https://bugzilla.redhat.com/show_bug.cgi?id=723708 ) which causes that the /etc/gdm/custom.conf has no effect. The closes workaround I find working on Fedora 20 is to totally disable listing of users (run as root): cat > /etc/dconf/db/gdm.d/01-mysettings
Read more

How to print a plain text file to printers from a terminal in Linux

Posted on

How to quickly print a plain text file to printers from a terminal in Linux? You can also use enscript: enscript – convert text files to PostScript, HTML, RTF, ANSI, and overstrikes https://www.systutorials.com/docs/linux/man/1-enscript/ enscript text-file The lp command can print a plain text file to a printer. My favorite command: cat text-file | lp -o
Read more

Linux timer sources

Posted on

Linux supports different timer sources and a machine can have multiple ones. How to find the available Linux timer source and the current one used? Find the current timer source: $ cat /sys/devices/system/clocksource/clocksource0/current_clocksource Find all available timer sources: $ cat /sys/devices/system/clocksource/clocksource0/available_clocksource