When user create a file or directory under Linux or UNIX, she create it with a default set of permissions. In most case the system defaults may be open or relaxed for file sharing purpose. For example, if a text file has 666 permissions, it grants read and write permission to everyone. Similarly a directory with 777 permissions, grants read, write, and execute permission to everyone.
Setting crontab every second
*/* * * * * script.sh
Boot sequence for X11/GUI mode/Runlevel 5 in Linux SysV Init
init Runlevel File Locations| Runlevel | Directory |
|---|---|
| 0 | /etc/rc.d/rc0.d |
| 1 | /etc/rc.d/rc1.d |
| 2 | /etc/rc.d/rc2.d |
| 3 | /etc/rc.d/rc3.d |
| 4 | /etc/rc.d/rc4.d |
| 5 | /etc/rc.d/rc5.d |
| 6 | /etc/rc.d/rc6.d |
When a Linux system running SysV Init begins to boot with its kernel, it first runs the /sbin/init program, which does some system checks, such as verifying the integrity of the file systems, and starts vital programs needed for the operating system to function properly. It then inspects the /etc/inittab file to determine Linux's overall mode of operation or runlevel.
Suid & Sgid
suid the particular command will run with the owner's permission not with the user's permission. No effect on directories.
sgid the particular directory will run with the group's permission. No effect on files.
suid the particular command will run with the owner's permission not with the user's permission. No effect on directories.
sgid the particular directory will run with the group's permission. No effect on files.
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