LinuxFix

ext4: No space left on device, but df -h shows free space

Fri, 23 Oct 2026 16:00:00 +0800

What you see

Writes fail, but df -h insists there is room:

$ df -h /var
Filesystem Size Used Avail Use% Mounted on
/dev/sda2 59G 41G 15G 74% /var

$ echo hello > /var/spool/postfix/maildrop/test
-bash: /var/spool/postfix/maildrop/test: No space left on device

Nothing was ever deleted to make room, and du -sh /var agrees there is space. The filesystem is not out of blocks — it is out of inodes, the fixed-size records that hold a file’s metadata. Every file, directory and symlink consumes exactly one inode, no matter how small it is.

Docker Socket Permission Checker

Fri, 23 Oct 2026 14:00:00 +0800

permission denied while trying to connect to the Docker daemon socket is not one error, it is four. This tool reads the two commands that separate them and tells you which one you have.

About LinuxFix

Fri, 23 Oct 2026 12:00:00 +0800

LinuxFix is a small reference site for Linux errors that are hard to read from the message alone: a systemd exit code, a 502 with a truncated upstream, a permission denied on a socket, a cron expression that does not fire when you think it should.

Contact

Fri, 23 Oct 2026 12:00:00 +0800

Email: linux@shenlijun.cn

Use it for:

A fix on this site that did not work on your system
A wrong path, flag, or default for your distribution
A dead link or a typo
A suggestion for an error that deserves a page

What to include

The faster the report is actionable, the faster it gets fixed:

Cron Expression Generator

Fri, 23 Oct 2026 12:00:00 +0800

How the five fields work

Field	Values	Notes
Minute	0-59
Hour	0-23	24-hour clock
Day of month	1-31
Month	1-12
Day of week	0-7	0 and 7 are Sunday

Each field accepts *, a number, a range (1-5), a step (*/15), a list (1,15,30), or a combination (10-20/2).

Privacy Policy

Fri, 23 Oct 2026 12:00:00 +0800

Last updated: 23 October 2026

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Docker: permission denied on /var/run/docker.sock

Fri, 23 Oct 2026 11:00:00 +0800

What you see

docker ps fails immediately with permission denied on /var/run/docker.sock, while sudo docker ps works. Nothing is wrong with the daemon.

Why it happens

The socket is owned by root:docker with mode 0660. Your user can read the file but cannot open it, because it is not in the docker group. A re-login is required after the group is added; an open shell keeps the old group list.

nginx 502: upstream prematurely closed connection

Fri, 23 Oct 2026 10:00:00 +0800

What you see

The browser gets 502 Bad Gateway. error.log contains upstream prematurely closed connection while reading response header from upstream, and the upstream: field tells you which socket nginx tried.

systemd: Failed to Start Service (exit code 203/EXEC)

Fri, 23 Oct 2026 09:00:00 +0800

What you see

systemctl status myapp reports a failed unit, and the journal shows status=203/EXEC. The service never reaches your application code, so there is no stack trace and no log line from the app itself.