Linux boots failed with “sulogin: can not open password database” while the /etc/passwd and /etc/shadow files look fine. How to fix this? The OS is Fedora 22. You may try this trick Step 1: boot Linux with rw init=/bin/bash following this tutorial. Step 2: after Linux booted, disable SELinux following this tutorial. Reboot. If it
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Category: Tutorial
How to manually set Vim’s filetype?
Posted onVim can detects the file types from quite well. But under certain situations, such as creating a new file, Vim does not automatically set the file type. How to manually set it? In side Vim, to set a filetype, set value to the filetype variable. For example, to set the filetype to php: :set filetype=php
How to transfer text messages from android to computer?
Posted onHow to transfer text messages from android phone to computer? One solution is to use the SMS Backup & Restore app. The app will backup your messages to a microSD card and then you can copy it out to a PC by connecting your Android phone to your PC with the USB cable.
How to get the latest git commit SHA-1 in a repository?
Posted onHow to get the latest git commit SHA-1 id in a repository? And how to get the first 8 digits of the SHA-1? Instead of the method introduced here, you may use $ git rev-parse HEAD to get the commit SHA-1 hash ID. If you want to get the first 8 digits only, use $
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How to debug media print view of Web page in Firefox?
Posted onHow to debug the media print view set by @media print {} in CSS of Web pages in Firefox? In firefox, after opening the Web page, First, hit “Shift + F2” to open the “Developer Toolbar” at the bottom. Second, in the “Developer Toobar”, input media emulate print and Firefox will show the print view
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How to sort lines by length in Linux?
Posted onI have a text file with many lines of text. In Linux, how to sort the lines by their length? You can make use of awk together with the sort program like awk ‘{ print length(), $0 | “sort -n” }’ /path/to/text/file Here, we use awk to calculate the text length and sort -n to
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How to make journalctl faster?
Posted onOn Linux, I check system logs by journalctl. But it is soooo slow. How to make it faster. By default without any options, the journalctl is indeed very slow. But usually, we are only interested in some logs and can use options to specify the logs that we are interested to check. This will make
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How to play video in full screen and keep it looping with MPlayer?
Posted onI would like to play a video file in full screen and automatically make it keep playing during an exhibition. On Linux, how to do it with MPlayer? You can use this command mplayer -fs -loop 0 video.mp4 Here, -fs make it fullscreen and -loop 0 makes it loop infinitely. For more usage of mplayer,
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How to do “contains string” test in Bash?
Posted onHow to test whether a string $str contains another string $needle in Bash? You can use this piece of Bash script: [[ “$str” == *”$needle”* ]] A usage example: $ str=”abcde hello” $ needle1=”deh” $ needle2=”de hello” $ [[ “$str” == *”$needle1″* ]] && echo “matched” $ [[ “$str” == *”$needle2″* ]] && echo “matched”
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‘dd’ command cannot support calculation for its parameters
Posted on$ dd if=/dev/zero of=./4Ktest100M bs=4KB count=25000*9 dd: invalid number `25000*9′ I think ‘dd’ should support calculation for its parameters like ‘bs’, ‘count’ and so on. You can get the effect by using some other tools/commands, like dd if=/dev/zero of=./4Ktest100M bs=4KB count=$((25000*9)) or dd if=/dev/zero of=./4Ktest100M bs=4KB count=$(bc <<< 25000*9) I think it makes sense. Thank
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How to remove trailing / in path in Bash?
Posted onI am writing a Bash script accepting input of a path from the user. I want to make the path have no trailing ‘/’, such as ‘/path/to/dir’ instead of ‘/path/to/dir/’. However, as the input is from the user, the input could be ‘/path/to/dir’. My script is intended to handle this. The question is: how to
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Why are keys overlap in SST files at Level 0 in LevelDB system?
Posted onAs is known, keys may be overlap in SST files of level 0 in LevelDB. I am wondering why it needs to be overlap? An sstable is read-only after being written to the disk from a memtable. Accumulated K/Vs in the log up to a certain size are organized as a memtable and written to
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How to attach and mount Xen DomU’s disk partitions on Linux without Xen?
Posted onHow to attach and mount Xen DomU’s disk partitions on Linux without Xen? You can use kpartx to create devices from the VM disk image (say, ./vmdisk0). To activate all the partitions in a raw VM disk image: # kpartx -av ./vmdisk0 This will output lines such as: add map loop1p1 (253:8): 0 497664 linear
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How to get a script’s directory reliably in Bash on Linux?
Posted onHow to get a script’s directory reliably in Bash on Linux? For example, to get the directory of the executing script $0. dirname can give you the directory name from the absolute path. You can get the absolute path of the script by readlink -f to handle symbolic links (consider a symbolic link ./run.sh linked
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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
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Why does ; after & lead to unexpected token error in bash on Linux?
Posted onThe command using ‘;’ after ‘&’ like ssh host1 hostname &; ssh host2 hostname & Leads to error like bash: syntax error near unexpected token `;’ Why does ; after & lead to unexpected token error in bash on Linux? And what’s the solution? The fix The quick fix is to change your command to
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How to add Google as the search engine in Firefox on Linux Mint?
Posted onIn Firefox on Linux Mint, Google is not in the list of search engines supported. How to add Google in Firefox on Linux Mint? Check this tutorials to add Google in Firefox on Linux Mint: How to Add Google to Firefox in Linux Mint as Default Search Engine
How to install Windows from USB drive?
Posted onI have downloaded the iso file of Windows 10 installation disk from https://www.microsoft.com/en-us/software-download/windows10ISO . But I do not have a DVD R/W drive. Whether and how to install Windows from a USB drive? You can use the Windows USB/DVD Download Tool to make a USB from the Windows ISO. Download and install the Windows USB/DVD
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How to manually kill HDFS DataNodes?
Posted onstop-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
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How to extract images from PDF on Linux?
Posted onI have a PDF file that has some images in it. How to extract the images out (not snapshot/screenshot of the page areas) from PDF on Linux? 2 tools that I usually use for extracting and saving images from PDF files: pdfedit and libreoffice. You can open the PDF file by the tools, right click
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