This is useful for debugging (hence programming related). On linux, we can use the command
strace -feopen python myfile.py
to figure out which python modules and shared objects are loaded. Is there an equivalent one-liner on macOS X?
I suppose you meant strace -fetrace=open?
dtruss -f -t open python myfile.py
Related
I mean I can't use it in bash, is it not available on OS X, or is it just missing on my Mac?
It's not a PATH variable issue, because I searched with find command, and there's no file named setsid on my Mac at all.
If it's missing on OS X, is there any alternative to it?
Or if it's the case that I somehow deleted it accidentally, where can I find a copy of it?
use Brew:
brew install util-linux
Yes. /usr/bin/setsid is missing on Mac OS/X.
The OS interface is available, so based on the chapter 2 man page there may be some hope for porting the Linux source to Darwin.
While macOS does not come with a setsid command, it does come with scripting languages which support calling the setsid C function, such as Perl and Python. So, if you don't want to (or for some reason can't) install a setsid command via Homebrew (or MacPorts or whatever), another option is to write your own in a scripting language. As an example, try this Perl script (which I based off this with some minor changes):
#!/usr/bin/perl -w
use strict;
use POSIX qw(setsid);
fork() && exit(0);
setsid() or die "setsid failed: $!";
exec #ARGV;
If you don't like Perl, Python's os module has a setsid function too.
A simple demo, which relies on the fact that /dev/tty is an alias of your controlling terminal if you have one, but reads/writes to it fail with an IO error if you don't:
$ bash -c 'echo I have a controlling terminal. > /dev/tty'
I have a controlling terminal.
$ ./setsid.pl bash -c 'echo I have a controlling terminal. > /dev/tty'
bash: /dev/tty: Device not configured
$
(Warning: With the release of macOS Catalina (10.15) in 2019, Apple deprecated the Perl, Python, Ruby and Tcl language runtimes shipped with macOS – they say new software should not use them, and they may be removed in a future macOS version – and Apple is not going to update their versions, which are becoming increasingly outdated. However, they are still there in Monterey, and while I haven't upgraded to Ventura yet, I haven't heard anything about their removal in that version either. One obviously shouldn't rely on them for any supported applications – if such software needs one of these runtimes, it should install its own copy of them. However, if it is just for a quick hacky script to easily test how some program behaves without a controlling terminal, using these OS-bundled runtimes is still fine.)
Is there a flock command on Mac OS X that manages file lock?
http://linux.die.net/man/1/flock
There is a cross-platform flock command here:
https://github.com/discoteq/flock
I have tested it and it works well on OSX as a drop-in replacement for the util-linux flock.
Perl one-liner:
perl -MFcntl=:flock -e '$|=1; $f=shift; print("starting\n"); open(FH,$f) || die($!); flock(FH,LOCK_EX); print("got lock\n"); system(join(" ",#ARGV)); print("unlocking\n"); flock(FH,LOCK_UN); ' /tmp/longrunning.sh /tmp/longrunning.sh
As a script:
#!/usr/bin/perl
# emulate linux flock command line utility
#
use warnings;
use strict;
use Fcntl qw(:flock);
# line buffer
$|=1;
my $file = shift;
my $cmd = join(" ",#ARGV);
if(!$file || !$cmd) {
die("usage: $0 <file> <command> [ <command args>... ]\n");
}
print("atempting to lock file: $file\n");
open(FH,$file) || die($!);
flock(FH,LOCK_EX) || die($!);
print("got lock\n");
print("running command: $cmd\n");
system($cmd);
print("unlocking file: $file\n");
flock(FH,LOCK_UN);
I don't believe that the flock command exists on OS X, but it does exist on BSD which should make it reasonably easy to port to OS X.
The closest that is available is the shlock command (man page), but it isn't as robust or secure as flock.
Your best bet may be to look at porting either the Linux or BSD version of flock to OS X.
macOS does not ship with a flock command, no, but you can install one via Homebrew (brew install flock). Which is probably the way to go if you need a shell script that can share a lockable resource with programs that use the flock system call to manage access to that resource.
If you are just trying to synchronize access to something and don't require compatibility with things already using flock, you could alternatively install procmail and use lockfile instead.
Just for completeness sake, you can compile flock(2) for OSX with some minor changes, i have not run any tests, but basic functionality works.
You can get the source from ftp://ftp.kernel.org//pub/linux/utils/util-linux. You then need to replace some calls to string functions not available on OSX, and you're good to go.
Here: https://gist.github.com/Ahti/4962822 is my modified flock.c of version 2.22.1, you still need the other sources for headers though.
You can install flock via conda, for example:
conda create --name flock flock
or
conda install flock
To install conda, see here.
Are you looking for flock the command line utility or flock the feature?
flock(1) is unavailable on OS X. flock(2) (the C function for file locking), however is.
Writing a simple command line flock(1) utility using flock(2) should be trivial.
You cannot write a shell-level flock(1) command for use in shell programming because of how file locking working. The lock is on the descriptor, not on the inode or directory entry.
Therefore, if you implement a shell command that flocks something, as soon as the locking command exits and the shell script moves on to the next command, the descriptor that held the lock disappears and so there is no lock retained.
The only way to implement this would be as a shell builtin. Alternately, you have to rewrite in a programming language that actually supports flock(2) directly, such as Perl.
Is there a fast way to check if a file handle is closed from the command line on os x?
lsof works, of course, but is super slow.
You´ll probably want to check out the DTrace Family man dtrace.
If you´re only interested on pure "file actions" you should have a look at opensnoop, which builds on DTrace and has been included since Mac OS X 10.6.
You can show all file in use by a process (by -p pid or -n name) and watch files with -f /path/to/file .
On Windows there is a tool Depends.exe to discover dependency of an EXE/DLL file on other DDLs. Which commandline tool is equivalent on Mac OS and Linux?
Mac OS X: otool -L file
Linux: ldd file
If those commands don't provide what you want, on Mac OS X you can dump all the load commands with otool -l file. On Linux you can dump the entire contents of the dynamic section with readelf -d file.
You can also try MacDependency (https://github.com/kwin/macdependency) which provides an UI replacement for otool on MacOS X. It shows complete dependency trees and the exported symbols as well.
try ldd in the terminal. This will provide you a list of dynamic libraries that the binary needs.
You can put something like following into your bashrc so that you can always use "ldd" as interface but it will redirect macos equivalent one if machine is mac.
# Macos equivalent of ldd
if [[ "$OSTYPE" =~ "darwin"* ]]
then
alias ldd="otool -L"
fi
I have a long running Perl script and I'd like to let it know (and report) how much memory it is using. I'd like to have this information both on Linux and Windows and if possible on Mac OS X as well.
These Perl modules could help you:
Windows: Win32::Process::Memory
Linux(and maybe Mac OSX): Linux::Smaps
This will show you how:
http://perldoc.perl.org/Devel/Peek.html
Also, http://perldoc.perl.org/perlguts.html
and, man pages for perldebug and perldebguts.
This is a quick and dirty and most of all CPAN-free method. It works on any OS that provides a /proc file system, that is Linux and Unix derivates, including Mac OS X, and also on Cygwin under Windows:
perl -e 'print qx{ grep VmSize /proc/$$/status };'