/usr, as you guessed, is the directory where "user" files reside; it contains all of the items that are not part of the system itself such as user programs and data. System programs are stored in /bin, user programs in /usr/bin, or, in Ubuntu, in /usr/share/. TuxFiles has a good description of the Linux directory structure.

2019年2月23日 · /usr ( from English "User System Resources" ) - catalogue/directory in UNIX-like systems, containing dynamically combined programs, user files and manually-installed programs. In accordance with FHS, it is mounted on root filesystem and must contain only data which is not to be modified by programs (that is to say, /usr in operational mode can ...

2015年11月3日 · /usr/local/bin is for programs that a normal user may run. The /usr/local hierarchy is for use by the system administrator when installing software locally. It needs to be safe from being overwritten when the system software is updated. It may be used for programs and data that are shareable amongst a group of hosts, but not found in /usr.

This makes a separate directory under /opt for every package you install, and that directory has all the requisites for the package (as opposed to /usr or /usr/local, where binaries for all the packages are under bin, libraries for all the packages are under lib, &c.). In general, if you're writing or packaging software yourself that needs a ...

This is a part where the FHS is slightly self-contradictory, as /usr is defined to be read-only, but /usr/local/bin needs to be read-write for local installation of software to succeed. The SVR4 file system standard, which was the FHS' main source of inspiration, is recommending to avoid /usr/local and use /opt/local instead to overcome this issue.

/usr/bin is for distribution-managed normal user programs. There is a /usr/sbin with the same relationship to /usr/bin as /sbin has to /bin. /usr/local/bin is for normal user programs not managed by the distribution package manager, e.g. locally compiled packages.

I don't see how #!/usr/bin/env bash is less secure. As I understand it, if an attacker has the necessary access to perform an attack against #!/usr/bin/env bash, they would also be able to perform a similar attack against a #!/bin/bash script simply by adding malicious versions of echo, grep, and the like to your PATH.

@EugenKonkov As stated, you can run apt-cache show python-is-python3 for an extremely detailed description. I don't think the description provided could be more to the point and concise, while fully conveying exactly what the package is and does.

2010年3月12日 · On Linux - pre-FHS 1 - you might have Python in /usr/bin/ or /usr/local/bin/. Or it might not have been installed, so you built your own and put it in ~/bin. Solaris was the worst I ever worked on, partially as the transition from Berkeley Unix to System V. You could wind up with stuff in /usr/, /usr/local/, /usr/ucb/, /opt/, etc.

Perhaps your main function has been commented out because of e.g. preprocessing. To learn what preprocessing is doing, try gcc -C -E es3.c > es3.i then look with an editor into the generated file es3.i (and search main inside it).