it seems the difference lies in handling of O_CREAT. # ls -ldn /var/tmp /var/tmp/hello drwxrwxrwt 4 0 0 183 Apr 18 10:37 /var/tmp -rw-rw-r-- 1 1002 1002 14 Apr 18 10:37 /var/tmp/hello
# echo 'howdy' >>/var/tmp/hello bash: /var/tmp/hello: Permission denied # cat /var/tmp/hello hello, world! # strace -f sh -c "echo 'howdy' >>/var/tmp/hello" 2>&1 | grep /var/tmp/hello | grep openat openat(AT_FDCWD, "/var/tmp/hello", O_WRONLY|O_CREAT|O_APPEND, 0666) = -1 EACCES (Permission denied) same permission problem with perl sysopen: # strace -f -e trace=file 2>&1 perl -e 'use Fcntl; sysopen(my $fh, "/var/tmp/hello", O_WRONLY|O_CREAT|O_APPEND); print $fh "howdy\n"; close $fh;' | grep /var/tmp/hello openat(AT_FDCWD, "/var/tmp/hello", O_WRONLY|O_CREAT|O_APPEND|O_CLOEXEC, 0666) = -1 EACCES (Permission denied) but success when leaving out O_CREAT (also removes the creation umask argument in openat call): # strace -f -e trace=file 2>&1 perl -e 'use Fcntl; sysopen(my $fh, "/var/tmp/hello", O_WRONLY|O_APPEND); print $fh "howdy\n"; close $fh;' | grep /var/tmp/hello openat(AT_FDCWD, "/var/tmp/hello", O_WRONLY|O_APPEND|O_CLOEXEC) = 3 # ls -ldn /var/tmp/hello -rw-rw-r-- 1 1002 1002 20 Apr 18 11:51 /var/tmp/hello # cat /var/tmp/hello hello, world! howdy Regards Matthias Ferdinand