It seems that occasionally GNOME can go a little screwy and its fancy mouse pointer plugin can result in an invisible mouse pointer. Which makes doing anything just a little bit tricky.
If you can open a terminal, enter the command :-
gsettings set org.gnome.settings-daemon.plugins.cursor active false
And all should be well. At least until it decides to turn itself back on again (so make a note of this fix!).
You have a a column of numbers that you have produced in some manner such as :-
$ awk '/clean message/ {print $(NF-1)}' mail.info.log
...
100935
12197
3606
84653
4498
99110
4762
3001
10889
12611
12249
12245
136599
49097
6668
And you want a quick and dirty way of finding the largest number. Well there is a way but it is perhaps the least efficient way to do it, and that is to sort the numbers into numerical order and use “head” to display the first one :-
$ awk '/clean message/ {print $(NF-1)}' mail.info.log | sort -rn | head -1
5476168
But frankly there must be a better method. And yes there is if you happen to be using zsh (or possibly others, but this has been tested with zsh). Simply iterate over the values assigning the current value to the “max” variable if the current variable is larger :-
$ max=0; for x in $(awk '/clean message/ {print $(NF-1)}' mail.info.log); [[ $x -gt $max ]] && max=$x; echo $max
5476168
You may be wondering why I don’t simply use the ability of awk to perform calculations. Well that is certainly possible, but I may not always be using awk to produce the numbers in the first place, and this is supposed to be a generic recipe.
Have you ever wondered if you can tinker with the ps command to change how and what is displayed? No? Well give up reading this post then.
I've known about ps for ages and also the way that the output can be tinkered with, but have not had an excuse to dig into it properly until I was looking for a way for ps to show the Linux container name for each process (don't get excited: ps -o machine is documented but not implemented at the time of writing).
If you read the manual page for ps you will be quickly distracted by all the different options available. These can be grossly simplified into three different groups of options: which processes to list, what to output, and how to sort the output.
This can be simplified down to almost nothing; ps on it's own lists just the processes running from the current terminal (window) :-
% ps PID TTY TIME CMD 2591 pts/17 00:00:00 zsh 13325 pts/17 00:00:00 ps
If you want to display all processes, add the "-e" option :-
% ps -e PID TTY TIME CMD 1 ? 00:00:03 systemd 2 ? 00:00:00 kthreadd 3 ? 00:00:00 ksoftirqd/0 5 ? 00:00:00 kworker/0:0H 7 ? 00:00:54 rcu_sched 8 ? 00:00:00 rcu_bh 9 ? 00:00:35 rcuos/0 10 ? 00:00:00 rcuob/0 11 ? 00:00:00 migration/0 12 ? 00:00:00 watchdog/0 (cut)
And lastly (not literally – there are other options), add the "-p" option to list processes by process ID :-
% ps -p 1 PID TTY TIME CMD 1 ? 00:00:03 systemd
By default the fields that ps outputs is somewhat peculiar until you realise that the output fields have been frozen in time. The default choice is somewhat minimal; and I'm not in favour of minimalism. And what use is the TTY and the TIME fields?
The TTY field shows you what terminal the process is running on – this was handy on a multi-user system where you could find out who was on what terminal and then write a message directly to their screen. A great way of winding people up, but not so much use these days. And TIME? We're no longer billed for the cpu time we consume, so the time spent running on the cpu is a rather pointless thing to list.
The "-f" option displays more information :-
% ps -f UID PID PPID C STIME TTY TIME CMD mike 26486 31092 0 21:24 pts/24 00:00:00 ps -f mike 31092 31091 0 20:11 pts/24 00:00:00 -zsh
But the output is still somewhat peculiar, and there are other more interesting fields to display.
There are various options for choosing the output format amongst a set of predefined choices, but the best bet is to ignore these and jump straight into selecting the individual fields that you want. These can be found in the manual page in the "STANDARD FORMAT SPECIFIERS" section. Simply list the fields you want after the "-o" option :-
% ps -o pid,comm,pcpu,pmem,nlwp,user,stat,sgi_p,wchan,class,pri,nice,flags PID COMMAND %CPU %MEM NLWP USER STAT P WCHAN CLS PRI NI F 28061 ps 0.0 0.0 1 mike R+ 3 - TS 19 0 0 31092 zsh 0.0 0.0 1 mike Ss * - TS 19 0 0
Obviously typing this in every time is somewhat less than ideal, but fortunately the authors of ps have already thought of this. By listing the fields within the PS_FORMAT environment variable, there is no need to specify -o :-
% export PS_FORMAT="pid,comm,pcpu,pmem,nlwp,user,stat,sgi_p,wchan,class,pri,nice,flags" % ps PID COMMAND %CPU %MEM NLWP USER STAT P WCHAN CLS PRI NI F 29440 ps 0.0 0.0 1 mike R+ 5 - TS 19 0 0 31092 zsh 0.0 0.0 1 mike Ss * - TS 19 0 0
To make this pernament, add this to your shell startup rc file; whilst editing you may as well set PS_PERSONALITY to "linux".
According to the ps documentation, by default the output is not sorted. In that case either my kernel's process table is remarkably well organised, or the distributions I use "cheat" and sort the output in process ID order. In the distant past where computers were shared amongst too many people, and the machines themselves were quite slow, it made sense for the output of ps to be unsorted. But it certainly doesn't make sense now.
And the ps command allows processes to be sorted by any field that you can specify in the "STANDARD FORMAT SPECIFIERS" section which conveniently enough you are now intimately acquianted. Simply add the relevant field to the –sort option :-
% ps --sort pcpu PID COMMAND %CPU %MEM NLWP USER STAT P WCHAN CLS PRI NI F 31092 zsh 0.0 0.0 1 mike Ss * - TS 19 0 0 31743 ps 0.0 0.0 1 mike R+ 5 - TS 19 0 0
With just a short list (and such a low percentage of the cpu in use) it doesn't make sense, but added to -e, it does.
Rather than change the default sort order, I personally prefer to configure aliases to do the job for me :-
% alias pscpu='ps --sort pcpu' % alias psmem='ps --sort pmem'
Preferring to use an alias here is rather convenient as there doesn't seem to be a way to configure the default sort order – officially there isn't one!
Reading through the ps manual page (during which you will notice many different options referring to old Unix varients) is a reminder of just how long and bitter the fight over which ps varient was the best. And now for a completely irrelevant picture :-
So there I was, wandering down the street thinking about :-
And I thought that it would be fun to knock up a little application that would pop up a window and show a file. Then I got real, and realised that the application was already written and allowed fancy formatting of the help file(s) – it's called a browser.
Now for a whole bunch of reasons, you probably don't want to use a full blown browser, but something a little simpler and without any fancy controls, and I plumped for dillo. Turns out that the "-f" flag turns off the fancy menu and toolbar, so what I needed was to persuade my window manager (Awesome) to run it when I pressed "Help" :-
awful.key({ }, "Help", function () awful.util.spawn("dillo -f /home/mike/lib/help-files/index.html") end))
If you need help adding that to your Awesome configuration file, you're in the wrong place!
And of course it works :-
(And now of course I need to spend some time writing some help files!)
Undocumented command options … grrr!
Every so often I find that I have a need to put a volume label onto a FAT filesystem – usually so a digital camera SD (or CF) card can be "automatically" mounted (actually they don't mount automatically on my workstation and I like it like that) in the right place. And of course every time I do, I remember that the command to do so is mlabel but I cannot remember exactly how to do it.
Because mlabel (together with the other mtools) has some sort of weird configuration file to turn Unix/Linux paths into drive letters‽ And yes that was an interribang although it could just as well be some other form of punctuation to express disgust instead. As it happens mlabel has an undocumented option to specify a device path … at least it doesn't appear in the usage hints :-
» mlabel -h Mtools version 4.0.17, dated June 29th, 2011 Usage: mlabel [-vscVn] [-N serial] drive:
It turns out that there is a "-i" option which takes a device path, but you still have to specify the drive as "::" just so things are less likely to go right :-
» mlabel -i /dev/sdi1 :: Volume has no label Enter the new volume label : LEICA1
And there it is!