Can write data and sync a removed file
124 views
Skip to first unread message
Benjamin
Dec 8, 2021, 8:25:50 AM12/8/21
to golang-nuts
The code is pretty simple, see below
I added breakpoints at line 18. I manually removed the file /tmp/db, and then continued to run the file. Everything was working well. Is this a bug or expected behavior?
Brian Candler
Dec 8, 2021, 11:13:31 AM12/8/21
to golang-nuts
As a general request, please don't post screen images. They are very hard to read, especially for (but not exclusively for) those with visual impairment. They also can't be copy-pasted.
You haven't said what platform you are running on. However if this is Linux or another POSIX-compatible system, it's perfectly fine to delete a file while it's open. The file remains on disk until the last process which has an open file handle has closed it.
You can demonstrate this quite easily:
- create a large (multi-gigabyte) file
- check the filesystem free space
- open the file
- delete it
- check the filesystem free space
- close it- check the filesystem free space
Only after closing the file will the free space be returned to the filesystem.
Benjamin
Dec 8, 2021, 12:10:00 PM12/8/21
to golang-nuts
I tested the program on both Linux and Mac, and the behavior is consistent. Makes sense, Looks like an expected behavior. Thanks.
Just paste the program as below,
package main
import (
"fmt"
"os"
)
func main() {
f, err := os.OpenFile("/tmp/db", os.O_RDWR | os.O_CREATE, 0666)
if err != nil {
panic(err)
}
if n, err := f.Write([]byte{1, 2, 3, 4, 5}); err != nil || n != 5 {
panic (err)
}
if n, err := f.Write([]byte{6, 7, 8}); err != nil || n != 3 {
panic (err)
}
if err := f.Sync(); err != nil {
panic (err)
}
if err := f.Close(); err != nil {
panic(err)
}
fmt.Println("Done!")
}
import (
"fmt"
"os"
)
func main() {
f, err := os.OpenFile("/tmp/db", os.O_RDWR | os.O_CREATE, 0666)
if err != nil {
panic(err)
}
if n, err := f.Write([]byte{1, 2, 3, 4, 5}); err != nil || n != 5 {
panic (err)
}
if n, err := f.Write([]byte{6, 7, 8}); err != nil || n != 3 {
panic (err)
}
if err := f.Sync(); err != nil {
panic (err)
}
if err := f.Close(); err != nil {
panic(err)
}
fmt.Println("Done!")
}
Marco Ippolito
May 4, 2025, 4:29:05 PM (5 days ago) May 4
to Brian Candler, golang-nuts
I wrote this shell script to exemplify the bullet points below:
#! /usr/bin/env bash
space() {
df -h /
echo
}
echo Space before creating large file:
space
echo Creating large file:
dd if=/dev/zero of=large_file bs=1G count=10
echo
echo Space after creating large file:
space
echo Opening large file in background process:
bash -c 'exec 3< large_file; sleep 10; echo Closing large file' &
pid=$!
echo
echo Removing large file:
sleep 1; rm -v large_file
echo
echo Space after removing large file:
space
echo Waiting for large file closure:
wait "$pid"
echo
echo Space after closing large file:
space
Which confirms expectations:
Space before creating large file:
Filesystem Size Used Avail Capacity iused ifree %iused Mounted on
/dev/disk3s3s1 228Gi 10Gi 188Gi 6% 425k 2.0G 0% /
Creating large file:
10+0 records in
10+0 records out
10737418240 bytes transferred in 5.169940 secs (2076894169 bytes/sec)
Space after creating large file:
Filesystem Size Used Avail Capacity iused ifree %iused Mounted on
/dev/disk3s3s1 228Gi 10Gi 178Gi 6% 425k 1.9G 0% /
Opening large file in background process:
Removing large file:
large_file
Space after removing large file:
Filesystem Size Used Avail Capacity iused ifree %iused Mounted on
/dev/disk3s3s1 228Gi 10Gi 178Gi 6% 425k 1.9G 0% /
Waiting for large file closure:
Closing large file
Space after closing large file:
Filesystem Size Used Avail Capacity iused ifree %iused Mounted on
/dev/disk3s3s1 228Gi 10Gi 188Gi 6% 425k 2.0G 0% /
--
You received this message because you are subscribed to the Google Groups "golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].
To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/db180a5a-71f3-4328-a50b-cea0f85bd174n%40googlegroups.com.
Reply all
Reply to author
Forward
0 new messages