On Fedora, after inserting/plugging in an exteranl hard disk with LVM partitions on it, the partitions will appear under /dev like /dev/lvm-group/lvm-partition. However, on CentOS 6, the LVM volumes do not appear automatically. How to mount LVM partitions from an external hard disk on CentOS? What you need on CentOS is to activate the LVM…
I want to run screen on a remote host on which I do not have root/sudo privilege and screen is not installed. I can compile or copy the screen program that can run on the host. However, it reports: “Cannot make directory ‘/var/run/screen’: Permission denied” As screen is not installed on the host, the directory…
I use curl to send requests to remote servers like following command. curl http://example.com/send –date-urlencode “data=hello” However, it is blocked by the network proxy squid in some networks with message like (some info anonymized with “…”): ERROR The requested URL could not be retrieved POST /… HTTP/1.1 Proxy-Authorization: Basic … User-Agent: Mozilla/4.0 (compatible;) Host: ……
The problem is like this: I would like to send a GET request using curl and the content has spaces, such as curl “http://example.com/send?msg=hello world” The space and the “world” will be left away if this command is executed directory on Linux. How to encode spaces in curl request URL? You can use the –date-urlencode…
One of HDFS cluster’s hdfs dfsadmin -report reports: Under replicated blocks: 139016 Blocks with corrupt replicas: 9 Missing blocks: 0 The “Under replicated blocks” can be re-replicated automatically after some time. How to handle the missing blocks and blocks with corrupt replicas in HDFS? Understanding these blocks A block is “with corrupt replicas” in HDFS…
I have a Linux box and it is connected to a network through a network adapter, say gate. How to find what is the current speed (10Mbps, 100Mbps or 1000Mbps) of the adapter? You can find the network adapter speed by the ethtool command: ethtool: query or control network driver and hardware settings For example,…
How to find a wireless adapter‘s speed in Linux? ethtool does not show the speed of the wireless adapters. For finding the configured speed of wireless adpaters in Linux, you can use the iwconfig tool. iwconfig: configure a wireless network interface For example, to find the speed of the wireless adapter wlp8s0: # iwconfig wlp8s0…
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…
How to sort all the files in a directory and subdirectories recursively by modification time on Linux? You can make use of find (GNU find, or plus stat), sort and sed together to achieve recursively sort files by modification time: find . -type f -printf ‘%T@ %pn’ | sort -k 1 -n | sed ‘s/^[^…
Where can I find a list of all Xen hypervisor command line options that can be passed to Xen hypervisor during boot? This page lists all options of Xen hypervisor: Xen Hypervisor Command Line Options
My program reports that the port is already used. How to find which program or process is listening on a certain port in Linux? You can use netstat to do this. netstat can print network connections. For example, to find which program is listing on port 9999 netstat -pln | grep 9999 You will need…
Unfortunately, my C: drive is almost full. Most of the space are used by the user home under C:Users. How can I move the home directory to another drive while not affecting the user’s usage of Windows. On Linux/Unix, moving the directory to another drive/partition and then keeping a softlink is enough. But how to…
I am using a shared network and scp to upload files. I do not want to use most of the bandwidth available. How to limit the network rate used by scp in Linux? You can use the -l option of scp to limit the rate of bandwidth. -l limit Limits the used bandwidth, specified in…
What suggested web browser in command line? This will be very useful for browsing the Internet from a command line via SSH. You may use Lynx, a fully-featured World Wide Web (WWW) client for users running cursor-addressable, character-cell display devices, in Linux. Homepage: http://lynx.isc.org/ Lynx is a fully-featured World Wide Web (WWW) client for users…
How to un-export an imported variable in Bash on Linux? For example, first, I export a variable MODE like export MODE=debug but I want to unexport the MODE (not turn to be `””`, should be truly non-defined). You can export -n MODE or unset MODE For your reference (from the [`bash` manual](https://www.systutorials.com/docs/linux/man/1-bash/)): export [-fn] [name[=word]]…
I got a password protected RSA private key with headers like (I have the password): —–BEGIN RSA PRIVATE KEY—– Proc-Type: 4,ENCRYPTED DEK-Info: AES-256-CBC,… How to decrypt a password protected RSA private key? You can use the openssl command to decrypt the key: openssl rsa -in /path/to/encrypted/key -out /paht/to/decrypted/key For example, if you have a encrypted…
A try like the following command failed $ sudo echo “echo hello” > /usr/local/bin/hello with an message bash: /usr/local/bin/hello: Permission denied It seems the writing to the file is executed under the non-root user. How to redirect STDOUT of sudo command on Linux and write the content to the file (/usr/local/bin/hello here) as root? You…
How to convert all text in a file from upper case to lower case and vice versa on Linux? Convert from upper case to lower case: tr ‘[:upper:]’ ‘[:lower:]’ < input.txt > output.txt Convert from lower case to upper case: tr ‘[:lower:]’ ‘[:upper:]’ < input.txt > output.txt
Any suggestions on good tutorials for screen on Linux? To start with screen: A quick tutorial on screen. After can use the basic functions of screen, you may check out A dummies introduction to GNU Screen and A guide to GNU Screen. During all the progresses, frequently check the screen man page.
Managing a cluster of servers, I would like to notified when a server is started. How to make the Linux servers email me or other admins automatically after they are started? I did this by adding a crontab entry on each servers like @reboot date | mailx -S smtp=smtp://smtp.example.com -s “`hostname` started” -r zma@example.com zma@example.com…