How to pipe the stderr to less
For example, try to less the error messages generated by the compiler with make | less Use this command: make 2>&1 | less or, if you want stderr only: make 2>&1 >/dev/null | less
Command line
How to list the functions in a .a library on Linux
How to list the functions in a .a library on Linux? You can use the nm command: The nm utility shall display symbolic information appearing in the object file, executable file, or object-file library named by file. If no symbolic information is available for a valid input file, the nm utility shall report that fact,…
Run cron jobs with environmental variables for an account
A common error for configuring cron is to use environmental variables for an account in the cron command. However, cron will run the commands without these variables defined. In the crontab -e, adding . $HOME/.profile before the commands play the trick. For example: 0 */8 * * * . $HOME/.profile; ~/bin/my-command Cron is started by…
Find out the number of CPU cores on Linux
How to find out the number of CPU cores on a Linux host. Use the command nproc. $ nproc nproc – print the number of processing units available: man page of nproc.
How to spawn a background process in a bash script
For example, I want to spawn many ssh background processes in one bash script: for i in `cat ./all-hosts` do ssh $i “ifconfig | grep Link” done Simply adding a & to the ssh commands does not work. Here is the script that works: for i in `cat ./all-hosts` do ssh $i “ifconfig | grep…
Force Linux to reboot
How to force Linux to reboot when the reboot command does not work. Enable the use of the magic SysRq option: # echo 1 > /proc/sys/kernel/sysrq Reboot the machine: # echo b > /proc/sysrq-trigger Even if you could not log on the system but sshd is working, you can force the Linux to reboot by:…
How to exclude certain repositories in yum?
This tutorial introduces how to exclude certain repositories in yum. Excluding certain repositories is needed usually. One example may be when you have several repositories that have the same package and you only want the one from a certain repository. For my situation, I choose to exclude the google-chrome and other repositories from Google when…
Plain text file pipelined to Linux mailx turns to “Content-Type: application/octet-stream” (an attachment)
Plain text file pipelined to Linux mailx turns to “Content-Type: application/octet-stream” which is recognized as an attachment by some email client. The command is like this: $ cat log.txt | mail -s “Updated log file” -r “from@example.com” “to@example.com” I expect it to be: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit But it turns out to be: Content-Type:…
Where are the Linux routing table entries stored on disk?
I know the routing tables on Linux is in memory after being set. However, where are the routing table entries stored on disk? I mean where are the routing table is persistently stored so that the routing table can be reloaded like the iptables (under /etc/sysconfig/iptables on Fedora/RHEL/CentOS Linuxes). If the system uses the /etc/rc.d/init.d/network…
How to repair a MySQL table?
After a server crash and restarting, MyBB reports a SQL Error as follows: MyBB SQL Error MyBB has experienced an internal SQL error and cannot continue. SQL Error: 145 – Table ‘./mybb/mybb_sessions’ is marked as crashed and should be repaired Query: SELECT * FROM mybb_sessions WHERE sid=’40021925bd0494ea31…’ AND ip=’x.x.x.x’ LIMIT 1 The dababase is MySQL….
How to use OCaml as a script language?
How to use OCaml as a script language like bash and python? It will be good that I can write a script in OCaml and directly invoke it. For example, I write a script named “script.ml” and then I can invoke it directly by $ ./script.ml Thanks! Three helloworld scripts: script3.ml #! /usr/bin/env ocaml print_string…
How to set Google Chrome’s proxy settings in command line on Linux?
How to set Google Chrome’s proxy settings in command line on Linux? I am using Google Chrome on Linux and start it by google-chrome. How can I set the proxy using the command line? It tell me that my desktop is not supported but I can set the proxy in command line. Use the –proxy-server…
How to restart Gnome 3 without closing the programs running?
What I want is to just restart Gnome 3 only and not to close and reopen the programs running. Thanks a lot! Just run r in Gnome 3’s “Run command” Box: Alt + F2, then enter r and hit Enter. Gnome 3 will restarts itself only.
Chrome’s KDE proxy integration broken on KDE / Fedora
Chrome reads the proxy settings from Gnome correctly. However, when I run Chrome under KDE, the proxy integration is broken: In the settings of Chrome, clicking the “Change proxy settings” opens the KDE proxy setting dialog correctly (the command kcmshell4 proxy actually is executed). However, after the proxy settings are made, Chrome does not read…
How to activate or deactivate a Linux host with Gnome remotely?
I have a Fedora Linux server with Gnome 3. I want to lock / unlock the remote Gnome desktop remotely. How to activate or deactivate it remotely through SSH? Use gnome-screensaver-command. It is not specific to Gnome 3. Turn the screensaver on (blank the screen): $ gnome-screensaver-command -a If the screensaver is active then deactivate…
How to merge a commit from another branch to my current branch in git?
I have 2 branches: dev and master. I have commits in dev like this: c0–>c1–>c2–>c3–>c4 Commits in master like this: c0–>c5–>c6 c2 and c3 fix a bug. Now, I want to merge commit c2 and c3 that fix the bug to the master branch, but I do not want to merge all the commits (e.g….
svn: how to clean up my repository directory?
I have a local svn repository. I work in the repository, e.g. compiling latex documents and building software packages, and there are many useless temporary files there. How can I clean it up by automatically clean these temporary files like the git clean -f in git? svn seems has no built-in function for this. But…
Make changes to sysctl.conf take effect without rebooting Linux?
I made some changes to /etc/sysctl.conf. I know it will take effect next time Linux boots. However, how to make the changes to sysctl.conf take effect without rebooting Linux? You can force Linux to reload the new configuration in /etc/sysctl.conf by: execute the following command as root: sysctl -p For more details, check the manual…
How to disable all swaps on Linux
How to disable all swaps on Linux to force the application/kernel use the physical memory? To diable all swaps on Linux, run this command as root: # swapoff -a -a means all swaps. Similarly, to enable all swaps on Linux: # swapon -a
Installing Dropbox on Linux
How to install Dropbox on Linux ? Just follow Dropbox’s instruction here: https://www.dropbox.com/install?os=lnx A quick command for 64-bit Linux: $ cd ~ && wget -O – “https://www.dropbox.com/download?plat=lnx.x86_64” | tar xzf – Use the dropx CLI:Â http://www.dropboxwiki.com/Using_Dropbox_CLI Download dropbox.py: $ wget -O ~/bin/dropbox.py “https://www.dropbox.com/download?dl=packages/dropbox.py” Set the permissions: $ chmod +x ~/bin/dropbox.py Start Dropbox: $ dropbox.py start Status:…