The “cached” total will also include some other memory allocations, such as any tmpfs filesytems. To see this in effect try: mkdir t mount -t tmpfs none t dd if=/dev/zero of=t/zero.file bs=10240 count=10240 sync; echo 3 > /proc/sys/vm/drop_caches; free -m umount t sync; echo 3 > /proc/sys/vm/drop_caches; free -m and you will see the “cache” … Read more
There is no such thing as an “open” UDP port, at least not in the sense most people are used to think (which is answering something like “OK, I’ve accepted your connection”). UDP is session-less, so “a port” (read: the UDP protocol in the operating system IP stack) will never respond “success” on its own. … Read more
These limits came from a time where multiple “normal” users (not apps) would share the server, and we needed ways to protect them from using too many resources. They are very low for high performance servers and we generally set them to a very high number. (24k or so) If you need higher numbers, you … Read more
One of your login scripts (.bashrc/.cshrc/etc.) is probably outputting data to the terminal (when it shouldn’t be). This is causing ssh to error when it is connecting and getting ready to copy as it starts receiving extra data it doesn’t expect. Remove output that is generated in the startup scripts. You can check if your … Read more
To find any expired repository keys and their IDs, use apt-key as follows: LANG=C apt-key list | grep expired You will get a result similar to the following: pub 4096R/BE1DB1F1 2011-03-29 [expired: 2014-03-28] The key ID is the bit after the / i.e. BE1DB1F1 in this case. To update the key, run sudo apt-key adv … Read more
apt-utils contains the /usr/bin/apt-extracttemplates program which is used when packages need to ask you questions about how to be configured. This package being Priority: important, means it should really be installed except in rare circumstances. If there is configuration pending, dpkg-reconfigure [package] will perform it. If you missed configuring a number of packages and don’t … Read more
I have had very good results using tar, pigz (parallel gzip) and nc. Source machine: tar -cf – -C /path/of/small/files . | pigz | nc -l 9876 Destination machine: To extract: nc source_machine_ip 9876 | pigz -d | tar -xf – -C /put/stuff/here To keep archive: nc source_machine_ip 9876 > smallstuff.tar.gz If you want to … Read more
Identify configured swap devices and files with cat /proc/swaps. Turn off all swap devices and files with swapoff -a. Remove any matching reference found in /etc/fstab. Optional: Destroy any swap devices or files found in step 1 to prevent their reuse. Due to your concerns about leaking sensitive information, you may wish to consider performing … Read more
$ ethtool <eth?> For example: $ ethtool eth0 provides: Settings for eth0: Supported ports: [ TP ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Supports auto-negotiation: Yes Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Advertised pause frame use: No Advertised auto-negotiation: Yes Speed: 1000Mb/s Duplex: Full Port: Twisted Pair PHYAD: 1 Transceiver: internal … Read more
With Unix you can pipe the output of one program into another. So to filter tail, you can use grep: tail -f path | grep your-search-filter