linuxprocessps
When I issue ps -elf|grep python for example on my system, I see these:
1 S 1000 6020 6008 0 80 0 - 9914 poll_s Jul12 ? 00:00:01 python manage.py run_gunicorn -t 3600 -w 8 -b 127.0.0.1:8000
0 S 1000 22496 22491 0 80 0 - 10477 ep_pol 12:32 ? 00:00:10 /var/lib/mywebapp/env/bin/python /var/lib/mywebapp/env/bin/pserve development.ini
What is the difference between poll_s and ep_pol?
For one, --help is not a command, it is an argument that is often given to a command to get help using it. Meanwhile, man is a command, short for "manual". Manual pages are installed by many programs, and are a common way to find help about commands, as well as system calls, (e.g. fork()).
If a program installs a manual page, it can always be accessed via the man command, whereas --help is just a common convention, but need not be enforced—it could be just (and only) -h.
man also typically uses a pager, such as less, automatically, which can make viewing and searching through the information much easier.
Finally, you mention Bash programming in your question—none of this is unique to Bash. Bash doesn't care about the commands themselves or their arguments for the most part.
Though it was down voted ... possibly because someone thought it was not answering the question ... I think @Rony's answer is a good start at explaining what the boot flag is about. (I was actually planning to begin my answer with an example similar to the one he provided.)
I was all set to ramble off an answer about how the boot flag is, at this point in time, an often ignored (as @Rony's example shows) historical remnant from a period when hard drives were smaller and bootloaders were much less sophisticated.
But then I discovered this had already been said in this answer to this question: What is the "Bootable flag" option when installing a distro?
What's more there was also a link to a short article about the Boot flag which says
When I claimed that the boot flag was a "historical remnant" I was assuming this was the case because clearly GRUB had no need to use it. Surely Microsoft would also have "moved on".
The well known quote usually attributed to Oscar Wilde turned out to be too true in this instance.
It appears that the MBR and PBR (Partition Boot Record) loaders used by the Windows operating systems DO expect the boot flag to be set correctly.
To test this I cleared the boot flag from all the partitions of a Windows 8 VM. (See below. If you're curious, here's a link to the pastebin of the complete BootInfo Script result)
Drive: sda
Disk /dev/sda: 26.8 GB, 26843545600 bytes
255 heads, 63 sectors/track, 3263 cylinders, total 52428800 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
Partition Boot Start Sector End Sector # of Sectors Id System
/dev/sda1 2,048 718,847 716,800 7 NTFS / exFAT / HPFS
/dev/sda2 718,848 52,426,751 51,707,904 7 NTFS / exFAT / HPFS
When I cleared the flag from both partitions, I got the error message FATAL: INT18: BOOT FAILURE when I attempted to boot. (I am not sure if that is from the Windows MBR bootloader or the VM's equivalent of a BIOS.)
Just to see what would happen, I also set the boot flag on the "wrong" partition, /dev/sda2 instead of /dev/sda1. Doing that resulted in the window shown in the image below.
<sigh/>
This experience makes me wonder if Microsoft is still using the same MBR boot sector loader which they used for MS-DOS and Windows 3.0/3.1?
Best Answer
To display a bit more of the
WCHANfunction name, you can use e.g.:This will show you the two functions are
ep_pollandpoll_schedule_timeout.The first is in
fs/eventpoll.cin the kernel, and is related toepollfacility, specifically to theepoll_waitsystem call.The other is in
fs/select.cand will be used both for the "plain"pollsystem call, and forselect.So they are both "waiting for something I/O-related to happen" wait states, but for different system facilities.