ssh client can use many authentication methods like password, keys. On a server, I set password-less log in with private/public key. Now, I want to try whether the new password is set correctly by log on using ssh. By default, the key-based authentication method is used again. How to force ssh client to authenticate using…
We know that we can disable USB 3.0 in the BIOS. But is there a way to force a USB 3.0 port to work in USB 2.0 mode inside of a running Linux? On Linux on some platforms booted in BIOS modes, you can use the following command to force USB 2.0 modes for your…
How to advertise a different router/gateway ip via DHCP in OpenWRT? In general, you need to configure the DHCP option with code 3 (router). (A list of all options can be found in http://www.networksorcery.com/enp/protocol/bootp/options.htm ) For example, to advise the gateway IP 192.168.1.2, you will send this option: “3,192.168.1.2” Now, for OpenWRT, you have 2…
How to export my Google Chrome password on Linux to a human-readable text file? In newer versions of Chrome, the passwords are stored using the encrypted password storage provided by the system, either Gnome Keyring or KWallet. We need to force Chrome to use a temporary profile folder with unencrypted password storage. Step 1. Connect…
How to find out a domain’s MX record for Email on Linux? For example, to find which domain/IP the email to gmail.com is delivered to. You may make use of the host command. The -t option is used to select the query type. type can be any recognized query type: CNAME, NS, SOA, SIG, KEY,…
The NFS server is down. It is reported “Stale NFS file handle”. I tried ‘umount’ and ‘umount -f’. But neither succeeded. # umount /mnt/store umount.nfs: /mnt/store: Stale NFS file handle # umount -f /mnt/store umount.nfs: /mnt/store: Stale NFS file handle How to force umounting the NFS without rebooting the Linux server? I usually have to…
Suppose we have two files, a.txt and b.txt . If we write anything in a.txt & b.txt, it should be redirected to c.txt. tee may help for this purpose. tee: duplicate standard input You may try a command like this: echo “hello” | tee -a a.txt >>b.txt Both a.txt and b.txt will contain the “hello”….
Firefox has multiple profiles and I am aware of choosing them by invoking firefox with the -P option. But I find that after one firefox instance under one profile is running, even I choose another profile during starting with -P, the new instance is still running under the existing profile. How to run firefox with…
I have some text files which contain some long lines. Now I would like to break lines to at most 80 characters. How to wrap long lines in a text file on Linux? The fold command can wrap lines. fold – wrap each input line to fit in specified width For your purpose, fold -w…
How to merge upstream into local fork repo with git? Merging an upstream repository into your fork: https://help.github.com/articles/merging-an-upstream-repository-into-your-fork/ Merging an upstream repository into your fork: https://help.github.com/articles/merging-an-upstream-repository-into-your-fork/
We have 2 static .a libraries and we would like to merge them into a single one for easier usage. How to merge 2 .a libraries to one .a library on Linux? With GNU ar, you can specify the single command-line option -M and control it with a script supplied via standard input, like the…
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…
On my Fedora 20, I find that the system automatically clean up file under /tmp/. This is convenient. However, it cause some problems for some programs. For example, HDFS puts its DataNode pid file under /tmp/ by default like hadoop-hadoop-datanode.pid. After it is cleaned up, the hadoop-daemon.sh script will consider there is no DataNode running….
How to configure Linux (am using Fedora 21) managed by systemd to boot to console (init 3) mode? systemd has the concept of targets as a more flexible replacement for runlevels in sysvinit. Runlevel 3 is emulated by multi-user.target. runlevel3.target is a symbolic link to multi-user.target. You can switch to ‘runlevel 3’ by running #…
Vim uses Xterm color codes like 9, 1 and 114 on Linux. What’s the overall mapping from color to codes or codes to color? Xterm color table: You can also find the Xterm color codes here.
How to deactivate a LVM logical volume activated by #vgchange -aay on Linux You may need to make a LVM volume group inactive and thus unknown to the kernel. To deactivate a volume group, use the -a (–activate) argument of the vgchange command. To deactivates the volume group vg, use this command # vgchange -a…
I keep seeing messages in dmesg as follows with “exception Emask 0x10” -> “SError: { UnrecovData 10B8B BadCRC }” -> “failed command: READ FPDMA QUEUED” -> “hard resetting link”: [ 7395.936692] ata4.00: exception Emask 0x10 SAct 0xe000 SErr 0x280100 action 0x6 frozen [ 7395.936701] ata4.00: irq_stat 0x08000000, interface fatal error [ 7395.936703] ata4: SError: {…
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: ……