Update heap size for Tomcat8 in Linux

If you install Tomcat8 (even tomcat7) via apt you will need to edit the file /etc/default/tomcat8   (or tomcat7) and look for the JAVA_OPTS variable. The Xmx value is there and you can set it as required.

Apache2 and php7 on Linux

To get apache2 working with php7 (or even lower perhaps?) on Linux you might need to download also the mod for php7


sudo apt-get install libapache2-mod-php7.0

Ubuntu 16.04.1 slows down while idle – kidle processes

Warning: the below might make your CPU run hotter or overheat – use at your own risk!

A new Ubuntu 16.04.1 installation – after short usage the computer slows down and the CPUs are about 50% busy. There are some kidle_inject processes running which take this valuable CPU.

Top shows the following:

 6898 root -51 0 0 0 0 S 47.1 0.0 1:20.16 kidle_inject/5 
 6900 root -51 0 0 0 0 S 47.1 0.0 1:20.38 kidle_inject/7 
 6894 root -51 0 0 0 0 S 41.2 0.0 1:13.55 kidle_inject/1 
 6895 root -51 0 0 0 0 S 41.2 0.0 1:16.90 kidle_inject/2 
 6896 root -51 0 0 0 0 S 41.2 0.0 1:18.28 kidle_inject/3 
 6897 root -51 0 0 0 0 S 41.2 0.0 1:18.64 kidle_inject/4 
 6899 root -51 0 0 0 0 S 41.2 0.0 1:20.02 kidle_inject/6 
 6893 root -51 0 0 0 0 S 29.4 0.0 1:08.23 kidle_inject/0

To stop these processes run the following command – it will disable them only for the current session. I very rarely reboot so I haven’t looked into making it permanent yet.

$ sudo rmmod intel_powerclamp


Add an alias on a network interface in Linux

$ sudo ip link set dev enp0s25 alias test
$ ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp0s25: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN mode DEFAULT group default qlen 1000
    link/ether 68:f7:28:84:38:ce brd ff:ff:ff:ff:ff:ff
    alias test
3: wlp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DORMANT group default qlen 1000
    link/ether 60:57:18:cf:0c:6a brd ff:ff:ff:ff:ff:ff

Enable export of all environment variables in bash

When setting up environment variables, for example in .profile you can write the following near the top of the file to enable exporting of all the environment variables without explicitly writing “export” each time:

set -o allexport

with the above, then you can just write the following, for example:


instead of

export TEST_DIR=/tmp/test

To disable the all export:

set +o allexport

You are also able to set environment variables without the export or allexport, however that will NOT make the variable available to sub-processes.

Count bytes and characters with wc

Count bytes and characters with wc

wc -c filename == counts the bytes
wc -m filename == counts the characters

this can be combined with other commands like grep, awk, sed

example with sed:

sed -n '1p' filename | wc -c

the above will print the first line from filename and count the bytes in that line

Fix ^M in Linux/UNIX using vi/vim

Sometimes if you edit a file in windows and then open it in Linux/UNIX it will have the special characters ^M at the end of each sentence. To fix ^M in Linux/UNIX using vi/vim run the following:

%s/[ctrlkey+v and ctrl-key+M]//g

sed tricks to replace multi blank spaces and tabs with single space

Replace all multi-blankspaces (more than one spaces/tabs) in file with mono-blankspace (one space):

sed 's/[<space>][<tab>][<space>][<tab>]*/ /g' filename

can also be:

 sed 's/[<space>][<tab>][<space>][<tab>]*/ /g' filename > newfilename

note: g in the end means GLOBAL

In the above samples, <space> means ‘ ‘ (empty space) and <tab> means ‘      ‘ (tab key press).

Sync servers using multiple streams with LFTP

If you have a remote server that you want to sync a directory you can use for example rsync, however rsync doesn’t offer the multi stream syncing and can be slower if you have many new files. The below solution uses lftp with 5 parallel streams to download and each stream is split into 10 separate segments. This is very helpful if you cannot max your download connection with regular methods and of course if the uploading server has enough bandwidth.

trap "rm -f /tmp/syncserver.lock" SIGINT SIGTERM
if [ -e /tmp/syncserver.lock ]
 echo "Syncserver is running already."
 exit 1
 touch /tmp/syncserver.lock
 lftp -u $login,$pass $host << EOF
 set ftp:ssl-allow yes
 set mirror:use-pget-n 10 
 mirror -c -P5 --newer-than=now-15min --log=syncserver.log $remote_dir $local_dir
 rm -f /tmp/syncserver.lock
 exit 0

The above sample should work for most cases – you just need to change the values of the variables (highlighted in red).

This part (–newer-than=now-15min) can be changed based on how old files you want to sync, for example if you synced the files 4 hours and you have new files in the last hour, you want to change this part to ONLY download the new files then change this part to be now-60min or more (but less than 4 hours in this example).

If you want to share from your local machine to the remote server, replace this line as (changed parts highlighted in red):

 mirror -R -c -P5 --newer-than=now-15min --log=syncserver.log $local_dir $remote_dir

Now save the above as a .sh file, example and you can add it as a cronjob to run every 15 minutes or run it when you have new files.

*/15 * * * * /home/redoer/ >> /home/redoer/sync_cron.log 2>&1
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