how to set linux date and time in commands
how to set linux date and time in commands For example, to change date to 14 Nov 2017 11:57:00, the command would be, $ sudo date –set “14 Nov 2017 11:57:00” Tue Nov 14 11:57:00 HKT 2017
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How to install alien on CentOS 7 to convert .deb to .rpm?
How to install the alien command on CentOS 7 to convert .deb to .rpm? alien is already in EPEL and it makes it quite easy to install it in CentOS 7. First, enable EPEL following this tutorials. Then, install alien by # yum install alien Then alien should be ready: # yum info alien Installed…
How to force a fsck during next rebooting of Linux?
How to force a fsck of a file system, say the root, during the next rebooting of Linux? 2 possible ways: /forcefsck way for / # touch /forcefsck and reboot. Next time the / will be fsck’ed . systemd way Add these 2 kernel boot parameters: fsck.mode=force fsck.repair=yes What these 2 kernel parameters do: KERNEL…
How to check interrupts lively in your systems?
I need to see what kind of interrupts are handled by which CPU. Please run command: # cat /proc/interrupts or you can execute $ watch -n1 “cat /proc/interrupts” to watch interrupts every 1 second. See [1] [2] for more details. References: [1] https://stackoverflow.com/questions/28301875/how-to-observe-interrupts-in-windows-or-linux-ubuntu-14-04 [2] http://www.linuxjournal.com/content/watch-live-interrupts
For QEMU/KVM, how to share data between host and guest
General question for developers to access data between VM and VMM. As I know, paravirtualization solution is a good way to share data for VM and VMM since it has better performance. Please use Virtio 9p solution for QEMU/KVM. Note that you need to load 9p related modules for guest kernel. Add following in your…
How to find out all files with replication factor 1 in HDFS?
How to find out all files with replication factor 1 in HDFS? The hdfs dfsadmin -report shows there are blocks with replication factor 1: Missing blocks (with replication factor 1): 7 How to find them out? You can run hdfs fsck to list all files with their replication counts and grep those with replication factor…
How to detect whether a file is being written by any other process in Linux?
How to detect whether a file is being written by any other process in Linux? Before a program open a file to processes it, it wants to ensure no other processes are writing to it. Here, we are sure after the files are written and closed, they will not be written any more. Hence, one-time…
How to get the highest temperature from all sensors in a server on Linux?
It is useful to monitor a server node’s temporary. Among all the sensors’ temperatures, the higher one may be a very important one. How to get the highest temperature from all sensors in a server on Linux? You can use this command to get the the highest temperature from all sensors in a server on…
How to check last boot’s systemd journal log in CentOS 7 Linux?
The command to check last boot’s journal log shows nothing on CentOS 7: # journalctl -b -1 Failed to look up boot -1: No such boot ID in journal Is the log stored and where it is? The reason this happens on CentOS 7 is that CentOS 7 by default does not enable the persistent…
How to print a line to STDERR and STDOUT in Bash?
In Bash, how to print a string as a line to STDOUT? That is, the string and the newline character, nicely? And similarly, how to print the line to STDERR? In Bash, you can simply use the echo command: echo “your message here” or echo your message here Examples: $ echo the message here the…
How to find the disk where root / is on in Bash on Linux?
Question: how to find the disk where the Linux’s root(/) is on in Bash? The root may be on a LVM volume or on a raw disk. 2 cases: One example: # df -hT | grep /$ /dev/sda4 ext4 48G 32G 14G 71% / For another example: # df -hT | grep /$ /dev/mapper/fedora-root ext4…
How to convert epoch timestamp to human readable date format in Bash?
In Bash, how to convert an epoch timestamp to a human readable date format? In Bash, you can use the date command’s -d option: date -d @<your epoch> Here @ specifies the epoch timestamp. One example: $ date -d @1490157520.05 Wed Mar 22 12:38:40 HKT 2017
Getting Hostname in Bash in Linux in 3 Ways
Getting the hostname of the node running a program can be useful in various scenarios, such as creating logs with the hostname, identifying which node a script is running on, or configuring a distributed system with different nodes. In Bash, there are several ways to retrieve the hostname of the machine, as mentioned in the…
How to get the epoch timestamp in Bash?
In Bash, how to get the epoch timestamp, the number of seconds passed since the epoch? In Bash, you can call the date command with format option “+%s”: date +%s Here, “%s” means: %s seconds since 1970-01-01 00:00:00 UTC
How to make sort using multiple threads to run faster?
sort supports –parallel N to run N thread. However, it seems it only uses around 100% CPU as I observed although the command specified that N threads can be used. The command is as follows cat large-file | sort –parallel `nproc` where I have 16 from nproc. How to make sort use multiple threads to…
How to convert svg to png in Linux?
How to convert a svg image file to a high-quality png file in Linux? inkscape works great with vector images (better than ImageMagikk’s convert). Try this command to convert in.svg to a 1000×1000 png image: inkscape -z -e out.png -w 1000 -h 1000 in.svg
How to get hostname in Python on Linux?
In Python, how to get hostname as the command hostname does on Linux? In Python, you can get the hostname by the socket.gethostname() library function in the socket module: import socket hostname = socket.gethostname() Reference: https://www.systutorials.com/dtivl/20/how-to-get-the-hostname-of-the-node?show=34#a34
How to put files with spaces in names into HDFS?
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…
In Bash script, how to join multiple lines from a file?
In Bash script, how to join multiple lines from a file? For example, to join the lines a good boy to a good boy You can use tr command, something like: tr -s ‘n’ ‘ ‘ < file.txt It just goes through its input and makes changes according to what you specify in two sets…
How to save the output of screen windows to a file on Linux?
In the screen, copying the history of the window output is quite hard. How to save the screen easily to a file? First type Ctrl + A then : to get to command mode. In the command mode, execute hardcopy -h /path/to/file screen will save the window output to /path/to/file.