What does chown 999 mean?

Question

I know what chmod (change mode) and what chown (change owner) do.

I also understand what the numbers mean after chmod do.

I was going through a docker tutorial and I saw chown 999 being used.

What does it mean and do?

Solution

who is the user 999? Is it just custom to him or a code used universally?

In Ubuntu and the Ubuntu family flavours, the numeric user ID in live sessions is 999. (The literal user ID is ubuntu, kubuntu, lubuntu ... xubuntu but in all these cases the numeric user ID is 999.)

When you boot from a USB drive, 'Try Ubuntu', you boot into a live session.

You can check with the command

grep 999 /etc/group

and you will find the user if you run a live session. Otherwise you will probably not find anything via that command.

The operating system used for the Docker tutorial is probably an installed system. And there seems to be a user ID with the numeric 999. It is possible to create such a user ID, but in an installed Ubuntu system there is no standard user with that numeric user ID.

Comments

[αғsнιη]

check this unix.stackexchange.com/q/418117/72456

[hassanzadeh.sd]

check this : stackoverflow.com/a/55241769/9533909

[YulePale]

who is the user 999? Is it just custom to him or a code used universally?

[Yaron]

@YulePale updated my answer, in my machine logstash has user-id 999

[Sergiy Kolodyazhnyy]

UID 999 is possible, there are other posts on askubuntu referencing this UID, but it may be specific to each system. stackoverflow.com/q/1013516 mentions UIDs below 1000 are reserved for system users, but there is no official list of what those users may be and POSIX apparently doesnt enforce UIDs either.

[Sergiy Kolodyazhnyy]

According to stackoverflow.com/q/4159910/3701431 even root user isn't POSIXly required.